It's still in Beta....so don't get too eager to use it...
Hence the 'free trial' - 13 days.
I'm not replacing MSE/Windows Defender with this new version. The current Malwarebytes works just fine with Defender.
According to their faq, that should work the same...no problems. Also, if you are a subscriber, you will be 'grandfathered' in to the final.