I have a GRT HX controlling a Trio Pro. This thing is amazing, it will fly the airplane from just after liftoff to cruise to minimums on an ILS or LPV, much better than I can hand fly it. But because it has so much capability, there is also a certain amount of set up and selection, i.e., button pushing. I?d be happy to demo it if you?re in the SF Bay area.
If you have an independent autopilot (Trio or TruTrak) I recommend controlling it thru the EFIS. Much easier, and, of course, for ILS or VOR approaches, necessary. But, for safety, try to keep current on how to run the autopilot independent of the efis (not possible of course if you use the GRT autopilot).
I?d be happy to try to answer questions about the Trio Pro; other autopilots, not so much.