A lot of pilots in General Aviation use all kinds of devices including portable GPS in their cockpits. The devices Cannot be Permanently Installed on the aircraft.
[Thus the C-Clamp]
I always preferred the boards, etc., that you strapped to your thigh. I found them the most convenient.
Back toward the end of when I was flying, LORAN became the latest and greatest. I imagine GPS is a quantum leap over LORAN like VOR was a quantum leap over 'A' 'N' navigation.
Woody