These are certified under TSO C4c and C113. Depending on who you talk to, the C113 requires an STC. There is no STC. IMHO, the FAA policy is bogus as they meet TSO C4c and should be able to be installed with a log book entry. Don't ask permission and you won't get denied. The battery backup unit has a similar issue, the battery has TSO approval, the system does not. This is a perfect example where innovation, safety improvement, cost, reliability are thwarted by FAA blind adherence to the rules. In this case they would make a European bureaucrat proud.
I suppose there is that whole can of worms about the model of primary horizon that appears on the airframe TCDS, or in the autopilot STC.
Take for example the TB20. I don't think the TCDS says anything, but the KFC225 STC definitely allows only the KI256. (For masochists, I think the KVG350 is also allowed 
) It does not allow the Castleberry exact electric equivalent of the KI256 (a very nice unit BTW). So the RCA unit could go on the RHS only, where AFAICS anything whatever could be fitted (including no horizon at all).
But if the plane has no autopilot, or the AP works off the TC (like e.g. the STECs) presumably only the airframe TCDS requirement is then absolute?
And if there isn't one, it's back to what you wrote...
I think there is a clear FAA statement that any "EFIS" product needs an STC, no matter where installed, but this isn't an EFIS.
I have it installed as a backup (with spare battery) for my Aspen. It is fully certified. I doubt it if I would like it as a primary
Nice panel, Commander
