With glass you have several instruments in/on one device, so you potentially lose redundancy.
Just to contrast; Airbus A320 family has fantastic glass, but has: 6 screens, 3 display management computers, 2 flight warning computers, 2 system data acquisition computers, and multiple power sources; All fed from 3 independent air data inertial reference systems, each with their own static, pitot and AoA vanes, 2 GPS systems and 2 OAT probes. Information can be switched to other screens in the event of a failed screen.
Not the same situation as a GA glass device and not the same 'mission' of course, but it just goes to show how much redundancy has been added. Glass can be wonderful but redundancy still needs to be there.
If one is relying on a single glass device, make sure your back-up instruments are both present and fully operational !
(Airbus still has back-up instruments as well as all that glass and redundancy).