The G900 aside, what exactly is it the LAA is doing? There are no requirement for an EFIS to be certified in an experimental aircraft. Do they look at the screens and say “like it” and “don’t like it” ? What about MGL EFIS. They are 100% user configurable, but probably have better electronics than any experimental Garmin. An experimental aircraft is not a certified aircraft.
They are checking for compliance with CS-23, which includes things like the direction indicator must be underneath the attitude indicator, the display must be readable in direct sunlight, the colour of warning indications must conform to certain norms, sensory cues that are equivalent to conventional instruments etc etc. The configurability of the MGL creates problems in respect of some of these.
Experimental aircraft in the sense of US experimentals don’t exist in the UK/LAA system. What we have is a lighter touch approach to regulation for amateur build aircraft that still uses the same standards as certified aircraft.
They are also checking for instruments giving misleading indications in some phases of flight. And there are some…