Fitting "non certified" avionics as secondary instruments
I was wondering whether it is possible to fit some of these non-certified avionics found in may permit aircraft to a CofA aeroplane as a "standby instrument"? For example one can pick up a pretty funky Dynon Skyview system for under 3000 GBP from Harry M's, which is cheaper than a certified MFD. If you could fit one of these in the P2 position as a "secondary" instrument, would this be legal. I'm thinking G reg and N reg here.
Some amazing pieces of kit out there a tenth the price of a G500, so it would make sense to have these as "backup" instruments while retaining the old instruments. I assume that as long as it didn't interfere with the certified avionics then it should be ok?
Ok, if it is NOT ok, then why can't one get an STC to fit one as a standby instrument, exactly the same was as JPI do with their range of EDM secondary engine monitors? I imagine if this was done under the FAA then the costs would be relatively low and fairly easy....??