Edit: So it seems some of these worked themselves out.  A couple were misinterpretations on functionality on my end. and some are still not working, still present, bugs, or feature requests.  I've crossed out those that arent an issue, and commented in italic on the solution, the reasoning, or an improvement.  Also bolded/labled feature requests as such.

For those in a hurry that might have a solution to offer for whats left on the board. 3, 9, 10, 11, 17, 18, 19
Much of those arent fixable without intervention on stardock's part.  but some might have a workaround or solution.

1) So far had the mouse disappear on me three times. once requiring a force close using the KB via task manager, the second and third time that didnt even cut it, had to log off and log back in.  thats the premiere issue as its happened three times in such a short amount of time.  No idea what causes this.

This is has not re-appeared since the initial day of setup which has left me worried that it will again at an inconvenient or inopportune time, but until such a time - i havent seen it in the last day or so after things got sync'd up and smoothed over between the pcs.

2) the cursor sometimes wants to stick on the right edge of the screen requiring me to back it off and "slam" it through so to speak. 

This stopped happening after some mucking about and restarting a few times, also noticed a setting which while was not toggled on, may have been glitched under the hood.  "require certain velocity for seamless" or some such.  Either way, should the problem return that's the first place ill look. 

3) the means of alignment is def inferior. not sure how free MwB does it, but regardless of the monitors size, resolution or position, moving through the center of 1 monitor moves through the center of the next.  With the alignment options in multiplicity I was able to get roughly center to center, but the minute you move up or down all bets are off when expecting it to be relative to the next screen if its size/reso is different.

4) it seems if your KVM'd into another pc,  you cant drag/drop files onto the window.  Was REALLY hoping this was the case, alas seems not possible.  I was going to live with dragging over via the seamless means, but when KVM'd in, it completely skips that pc and moves onto the next if i try to do so.  Argh!

 Seems you can copy/paste into a KVM, I can live with that.  But the addition of drag/drop would be an improvement for sure.  Feature Request!

5) cant designate a monitor to open the KVM on.  You can move it easily after opening of course.  Still I do all my work on one monitor, and all my gaming/virtual machines/remote stuff that requires real estate on the other.   For some reason multiplicity is identifying my monitor 2 in windows as my monitor 1 and always opens the KVM there, right on top of everything.   Its an extra step/annoyance to move it over each time.  tarnishes the experience.

Seems to open on whatever screen has your focus at the time of initiating the hotkey.  Would be great to set a default screen to open on if your workflow had that requirement.  Feature Request!

6) no dynamic switching (that i can tell).  move between pc's physically sometimes, and to be able to use any keyboard and mouse for any of those pc's was something I was used to.   Mouse without borders does it.  Synergy does it.   This at the 100 dollar price point, does not. 

Now that ive had time to go through this more thoroughly on several pc's, it seems like a means to try and glean more license fees   I hope im wrong considering several much cheaper softwares operate this way out of the box.   Currently to afford control to another pc not designated primary, you need another license.  (or so it says when you attempt to toggle on what appears to be the related setting)

7) connecting to a pc that has the monitor in standby (due to the 10 min timer) you get a black screen lol... you have to actually wake your monitor before connecting? 

This is due to my particular blend of "Blank" screensaver and standby.  I had the default 10m monitor standby, but I had the built in blank screensaver set for 5m.  So if it was a short second away from the pc i could resume much faster than waiting for the monitor to wake itself up again.  Nonetheless, multiplicity seems to play well with standby, but not the blank screensaver.   Shaking it out of that via KVM proved difficult or problematic.

8) default to stretch mode doesnt work (minor but anything not working in software of this caliber isnt confidence inspiring) 

<from the manual> "This setting will set the default preference for new connections to stretching the screen contents to fit the resolution of the local screen. If you had specified a preference during the last successful connection, this will not override that setting."  i guess this will only work the first time on brand new connections? and if you change it afterwards your borked?  Not sure there's much a point to this setting then.  It potentially saves you one click the first time you connect to a pc?  Maybe a rework to the functionality in that it should always open to stretched if toggled.  always open to 1:1 otherwise.  Or some similar implementation.

9) no option for mouse return point on seamless?  if you have something running on your left side of one screen and you pan through, the cursor is left there on the left.  it gives focus to whatever is running there and if its something that prevents your display from sleeping (and thus pc from sleeping) no bueno.   A return point, something simple like a box for return to center etc would be nice.  Feature Request!

10) Wake-On-LAN doesnt seem to work at all.  HUGE DISAPPOINTMENT. tried it a dozen times and didnt wake up my laptop.  works through teamviewer & through wake-on-lan/magic packet UWP app as well as from my phone fine.   Checked the mac address in multiplicity just in case.  Tried with use IP on and off.  Trial limitation?  

Nope, i went ahead and purchased with optimism toward future updates.  Unfortunately even with the full version, WoL doesnt work. and since as i've added below, neither does prevent sleep when using primary. Looks like i get to use one of my other apps to wake it first.  Some maybe relevant info here https://forums.stardock.com/497027/page/1/#3770792

11) the configure settings window doesnt save position.  Ideally i'd be able to open it on an accessory display while gaming fullscreen on my main display.  minor but most modern day apps save window location.  Feature Request!

12) screen darkening seems to not work if it does what i think its supposed to do?  black out a screen or dim/alter it when connected? 

It does work, but requires being enabled on the primary, I had construed "opt-out" as meaning it was enabled by default.  Still oddly enough, can be opted out of on secondaries but not primary........like the feature but not enough to deal w/ my main pc going dark if used without an option to opt that one out.   Feature request!

13) ugh! another big one.   Appears audio sending is perpetual?  I figured it would send audio if your connected, but apparently it sends it if your connected or not.  the indicated ctrl+f12 key to toggle it doesnt seem to work.  So this leaves you with one option, leaving another icon in the tray.  (coulda integrated it with the main tray icon imo) 

So it seems this works, it just takes a few seconds to engage.  If you have your desktop sound icon enabled, watch for it to mute on the kvm'd pc.  Its not instantaneous and it takes longer than you would expect.   Dont press the key again thinking its not toggling.  This is what I did initially and all it did was cause confusion and frustration.

14) press ctrl 3x to mirror input not working at least not how i understand it to?

Works.

15) any way to be connected to more than 1 pc at a time?  I coulda swore i saw a screenshot showing a tab-like interface so you could quickly swap between multiple simultaneous connections.  Doesnt seem to be so, would be a KILLER feature.  Could multitask several other PC's at once similar to the way you can work between vm's in vmware.  Build on the groupy aesthetic and use that top bar   

This is in fact possible.  Just not intuitive.  You have to re initiate KVM mode and re-connect.  Its not integrated into the KVM controls in any way, multi-initiation nor fast switching between (tabs).  I am also a groupy user so i was able to smoosh the two together and get something semi functional, but it would be far superior if it was integrated into multiplicities control bar, so you could fullscreen your kvm's and still swap. Feature Request!

16) alright guys.  I didnt want to come into this too critical.  I really want to like it as i LOVE groupy and start10 and i was becoming a fan.  but for 100 bucks i mean cmon.   I just tried to test the copy and paste feature even, with a simple blank text file.   You would think it was instantaneous or close to it right?  Nope, it said copying file, and a bar went across, and right before the end, it reset, and did it again and again and again.   The only way to stop it was to unload multiplicity.  

Some kinda bug, similar to the whole disappearing cursor thing.  After some restarts etc, it hasnt reappeared. 

17) another biggie.  Prevent secondary computers auto sleeping whilst using this computer.  After typing out some work emails, i look over and poof back asleep.  I imagine this not working is related to why on earth Wake-On-Lan isnt working.  It likely uses the same communication line to keep the others awake. 

18) no win key as a modifier for hotkeys.  doh!  Feature request!

19) gah, just finished going through everything.  no hotkeys able to be set for toggling the sound streaming on and off apart from the default.  Was hoping to be able to set a custom one.  Also no hotkey assignable to shortcut KVM connection to another pc.  Even a hotkey for Wake on LAN (if i could even get it to work).   Shame. Hotkey options definitely could use some expansion.  Feature Request!

20) and to finish it off with a round number 20.   When connected to another pc you have the big ole disconnect bar in the center, and then an X next to it that does the entirely same thing?  thats kicking redundancy up a notch.  I realize this is almost purely aesthetic and may seem nit-picky, but ive posted it anyways for a few reasons.  1) im a stickler for polish.   2) I could be completely wrong and the functionality between the two buttons could be different and id love to know.  3) i needed a round number 20 and after spending all day and going through this inside and out, i think ive found everything.

This one is on me.  Long day, resolve waning etc.  They do marginally different things.  The center banner/disconnect button takes you back to the connect screen.  The X takes you back to the desktop.

21) baaaaaaah.  so much for my round #20.  So i noticed the setting (render at xxx resolution if no monitor present).  I had hoped that meant I could turn off the monitors on my other pc and still connect and get an image.   I do... a pure black screen.   Evidently a monitor literally cannot be present, if its connected and in standby, or connected and turned off.  You get black?

This was related to #7.  The short, disable screensavers.

22) means to re-enable the action center notifications?  Once theyre disabled, they no longer show up in windows 10's notification list should you wish to re-enable them.   Someone kindly point me to the registry string?

Looks like you can re-enable them if you have your settings>notifications open and you close & re-open multiplicity.  You need to immediately refresh the notifications list, or microsoft? takes it upon itself to remove the notifications toggle for multiplicity rather rapidly.  If anyone knows where the registry string is for this, it would be appreciated.  I had a look around but nothing stuck out. 

23) After restarting my laptop, seamless'd my way over there to log it in, and while it was starting up - it literally held onto my mouse cursor.  I couldnt bring it back to my pc.  Never happened with the almost half dozen km's ive used in the past.  My slow laptop with a mechanical HDD rendered me useless at my main pc for far too long.

I'm gonna check this one off.  If i log-in and zip my mouse out of there fast it seems to circumvent it.   That or it was related to one of those initial set-up quirks and between restarting all the secondaries has worked itself out.  Not gonna push my luck to test it, but doesnt seem very pressing of an issue.

Id love to get the feeling that development on this is active, and the staff are involved in actively trying to squash bugs and improve their software.  However given the length of time this has been around, and how important some of this stuff is..... meh.   Doesnt seem to be much staff activity in these parts.  Shame.  As i mentioned, I was finding myself a pretty solid stardock fan, and they certainly have found their niche.   Time will tell. 

In the end I'd say this needs a really solid run through and update by a seasoned developer.  ESPECIALLY given the price premium. >.<