Five years ago I settled on dual HDX, dual Dynon ADAHRS, Dynon autopilot, GPS175, GNC255, GTR200 (second radio), Dynon autopilot control panel, dual alternators, single battery, backup batteries for both HDX’s.
The Dynon autopilot works well in Expert mode, but has some mode menus that cause me go into “what is this thing up to now “ mode. The connect and disconnect sequences, what is engaged and what is not seem particularly unique to Dynon. Compared to the quality of Garmin documentation, Dynon documentation is definitely written to a lower standard.
Another consideration is charts, software support, developing and loading flight plans.
HDX only supports Seattle Avionics charts, so I need an annual subscription for SA charts. For the GPS 175 I need a separate subscription for charts and approaches because Garmin does not support SA charts. For flight plan preparation I had been using FlyQ on an IPad which works well for the HDX but doesn’t work for the GPS175 so I use Garmin Pilot for loading the GPS175 flight plan - yet another subscription.
I wish it all worked seamlessly ,but it doesn’t, not with my configuration.
If I were going to start over with a new design and planning on a fully capable IFR aircraft I would probably go with dual G3 and a Garmin autopilot. I did single pilot IFR in a Cardinal for many years - I wouldn’t consider doing IFR in an RV without a working autopilot that had a high probability of being available and doing what I wanted for the whole flight. I consider myself a very average pilot getting on in years so my tolerance for high workload and stress is much lower than it once was.
Going through the motions of planning a flight, arm chair executing the flight, considering all the likely failures and how you will deal with them is a good start to getting to the configuration you will be happy with.
Keith Turner