"Aren't that hard" is a matter of perspective.
I've used many types of air couplers, while some are more of a PITA than others, ones I've had no difficulty with are potentially dangerous to my father (he's in his 80s).
If you follow the link posted earlier about "answers" there is a YouTube video linked with a "force test" of a Milton V coupler.
The author uses a load cell to push the coupler to full engagement, it took over 400Lb of push.
Not a problem if you are the only one working in there, but if anyone you care about, with less upper body strength than yourself, uses any compressed air, you may want to exercise great care in choosing your couplers.