I gave a Hennesey UL a go one summer. a few of my thoughts.
They are probably great for a back sleeper and Ok for a side sleeper but don't really make the grade for a belly sleeper.
I tried with both a pad in the hammock (One of those 1/4" extra wide models)and JRB under quilt. In anything but hot summer conditions you will need under insulation. My feeling was that the under quilt worked much better than the pad, but as I do longer distance hiking, not having a pad sucks when you want to stay in a leanto/shelter or are above tree line and have to go to the ground. The tarp with the Hennesey wasn't really big/cut right to make a good ground shelter with trekking poles.
Once you add in a under quilt, the whole combo weighs as much or more than a light tent (ie a TT contrail).
On the other hand if you can deal with the other stuff, it was a bug proof shelter you could set up anywhere, great for eastern hiking where the woods are thick and you might want to do some stealth camping in an area without a clearing to set up a tent.
