OK, I'll chime in with what admittedly is a HIGHLY biased opinion...
If going GRT, go ALL GRT.
Here's the story of the evolution of the panel in our Glasair Sportsman.
First it was a basic VFR panel with a GRT Horizon WS display and TruTrak ADI autopilot and AF2500 engine monitor... Before the panel went into the airplane a whole bunch of changes were made. The Horizon became and HX, the autopilot became a Vizion, the standby steam instruments became one of the first production batch Mini-X devices. Along came first and subsequent flights. While I loved the AF2500 I suffered a confidence-killing event in the air at night - an attitude miscompare between the HX and Mini-X. I didn't have a tie-breaker source of attitude and the only real estate available in the panel was taken up by a dedicated engine monitor screen. As much as I loved the AF2500, it was replaced by a Sport EX EFIS over on the right side of the panel, and, behind the panel, a GRT EIS-66R remote engine monitor was installed.
In this entire installation the weakest link is the EIS-66R, and only because it has a couple of idiosyncrasies relative to its EIS-4000 brother. As an example, it's internal MAP sensor cannot be calibrated, thus engine percent power is always off (by 3% in my case).
This final configuration, Mini-X, HX, Sport EX and Trutrak Vizion make a cockpit which is extremely capable, well integrated and a delight to fly. Speaking of which, the Sportsman is pre-heating right now so I can go for a quick flight!
My recommendations if buying a GRT device would be:
- buy as many serial ports as you can... remember things like the external GPS receiver will ADD ports rather than cost you ports
- Synthetic vision is a must-have - I can't believe how much more intuitive it makes navigation and flying in general
- sensed AOA is a total no-brainer - hook the audio output to your audio panel so you can hear the tones - fly the wing by using your ears while keeping your eyes outside the cockpit
- get their dual-frequency ADSB receiver so you have a full picture of ADSB-based traffic, available both on the GRT screen as well as on external tablet devices