What is the advantage of PEX pinch clamp vs. crimp rings?
The benefits of the clamps are exactly as you say - the biggest one being that they're sometimes the only option in a cramped area. They used to be over 5x the price of the rings, which adds up very quickly -- but I see now they are only slightly more expensive.
I don't think they're any less reliable than regular pex crimps, I know of some (at my cottage) that have been fine for 5+ 10+15+ years now.