If you check the planet data card, you can see the resource rates for the asteroids go up and down as you switch the trade ports in/out of resource mode.

Dunno how/if the autocast works though.

I was having problems with these as well. When I toggled it to focus resources I noticed the trade ship that launched from it just stopped. Are these supposed to act like refining ships? Also, there was no indication that these were actually helping crystal/mineral extraction. Hovering over the resource that usually shows income from TEC refineries showed nothing for the Advent. Is there any way to tell if they are working, or just toggle it and assume things are going as planned? The autocast option is annoying as well, usually had it disabled as this seemed more like a toggle option rather then something you want switching out on it own.