As mentioned, there was compatibility between some model(s) of the TRIO and NAVAID servos. I think they were the ONLY ones to do that.
TruTrak servos quickly became the "standard" some years ago. GRT and I believe DYNON then made servos that could use the Trutak mounting approach so if you had a TT, it would be easy to sway out those servos for ones supported/driven directly by the DYNON/GRT EFISes.
The GARMIN mounting approach to servos ended up being different.
Soooo.... if you want to use EXISTING servos, TRIO is your option.
Otherwise you need a lot more product and it all depends upon what will fit and how much money you want to spend.
p.s. I started out with the NAVAID many years ago and eventually switched to GRT alfter almost doing TruTrak after deciding NOT to use a "System 30".