Garmin lists the G5 as a Primary Flight Instrument. For experimental gliders without specific equipment lists it should be fine to replace the steam gauges (at least that's the way I'm reading Part 23 regs). It may well be more complicated than that & I'd definitely want the battery backup. It's a pretty attractive option, especially having the AHRS.

Craig
7Q

You referee to what specific FAR Part 23 paragraph?