I went to look at one with a friend who was interested. There were certainly advantages, as everything was conveniently set up, very attractive and cosy, own little garden patch and shed. It was very quiet and peaceful (over 50's only, no pets allowed).
It would virtually eliminate all the hard work of housework/maintenance/upkeep that houses require and be a good base for somebody who likes to go out or relax.
At the site, you were tied into buying your gas from the owner, contributing to the water bill etc. and there were many rules.
What put us off, though, was the thought of tripping and slipping to the car parking space (not very near the home) in icy winter conditions (and back, with shopping) although it all looked beautiful in summer.
No, of course, they're not good value for money, but they really do suit some people, which is far more important.