No comments on the technical side, but I sometimes instruct on a G5-equipped two-seater and these two things struck me:
- I find myself looking at the ASI more often than at the speed tape of the G5. There may be a small discrepancy between the two sometimes (no more than 3-4 kt at most) but I find that the needle on an ASI is better at showing me the trend (rough location of the needle shows me where I am on the speed scale, and movement, slow or fast, shows me what speed I'll be at in a few seconds time) without having to interpret the digits on the G5 speed scale.
- From the righthand seat, the G5's bezel actually obstructs the view of the ASI's righthand side, making it harder to use it from the instructor's side. This will not be a problem if you're going with G5s on both sides, but keep it in mind if you install them on the left side only.
One positive aspect of a G5 for me: I can switch it off if I want to make sure that my student flies attitudes based on what he/she sees outside, instead of on the AI... so no more messing around with bits of card, post-its or dedicated instrument covers.
More of an issue during VFR instructing of course.