Carryfast:
Palm couplings are the solution they also contain the valve still no need for taps but no need to struggle like silly C couplings.
Ironically we had Palm couplings on all our vehicles for a while and were even more advantageous on drawbars no need to struggle at ground level and immune from road dirt and salt.Then they reverted to bleedin C couplings.
Badly maintained C couplings will seize up and be difficult to detach or fit on. True.
Badly maintained palm couplings will leak, and may detach too easily.
Properly fitted and maintained, both work, but the C coupling seems more of a fail-safe option to me.