I'm about 20 stone and have a top 'strength' Blackbird, I'm 6foot 2 inches. Got it about 3 months back, used it once and it was a bit nerve wracking. The rings slipped once which didn't fill me with confidence although I was more worried about damaging the webbing/hammock than myself. TBH biggest issue (aside from too many sausage rolls and cans of lager in my lifetime) was psychological and probably technique in setting it up.
I found it incredibly comfortable when I just lay in it and relaxed, almost drifted off in the afternoon. When I tried to get to sleep (using 1 big wool blanket on top and travelling rug under) I was cold. Ended up using my sleeping bag which was dammed awkward.
I decided I was probably a rabbit than a squirrel at heart (ground not trees).
Next time I go out with it, I'm going to use it to relax in to get used to it and take a mat and bivy for sleeping on ground. I can see even from my limited attempt that it could be a great system to use. Until I get a bit more 'training' I'm going to take a dirt nap.