I installed an Avidyne IFD550 (plus Avidyne's ADS-B in/out that they threw in with the deal) into my Piper Cherokee Six 300.
I didn't cut my teeth on Garmin, so I'm not biased and like Garmin gear. I stopped flying in '94 and started up again only a couple years ago when I got my instrument ticket.
I routinely use the RealityXP GTN750 in simulation and an actual 750 while flying in my buddy's 182, so I have an idea of the operational differences.
1. Reliability? My install is only a year old, but the 550 has performed flawlessly.
Everything just works with it hooked up to dual Garmin G5's and my legacy Piper autopilot. In fact, I have no incentive to upgrade to a newer autopilot with this setup.
2. Support: Every time I've called Avidyne for support, they've gotten back to me by phone and answered my questions. I'd give them high marks here.
3. User Interface: Having the extra physical buttons is extremely handy vs. always relying on a touchscreen. I've flown from Boulder, CO (BDU) to Teterboro, NJ (TEB) day and night, in smooth and bumpy air, with plenty of actual. The 550 was very easy to manipulate in all conditions. I ran into some issues with the GTN750 flying "over the rocks" to Steamboat Springs in my friend's 182 when things got choppy.
I also like how easy it is to program and modify flight plans on the Avidyne. If you're already a dyed in the wool Garmin person, you may be more comfortable with their interface. I never learned the Garmin 430/530, so I don't have a frame of reference.
3. Cost: I think you can get better deals on the Avidyne gear. Interesting that Bendix-King includes Avidyne in their product suite. The one issue I have is the Jepp data required by Avidye does seem a bit more expensive than Garmin's data. That's my only negative.
Buck
Those of you that have IFD’s, how have they been from a reliability standpoint, and how has the customer service been? The only bad stuff I have heard about Avidyne equipment has been from staunch Garmin people, and I would like to get some real data.