I bought a Hennessy hammock last year, but have yet to spend a night in it. I did try it out in the store before I bought it. The trick is to sleep diagonally in it, i.e. with your feet on one side of the centreline and your head in the other, in which case you lie almost flat. Now personally, I like to sleep on my side and I'm a fairly restless sleeper, so I don't know whether I'll be able to actually sleep in it.
My intent when I bought it was to sleep in it one night and, if I couldn't stand it, return it to the store for a refund. (They suggested this, by the way - better business for them.) Well, I couldn't find a place to sling it that weekend, one thing led to another, fall turned into winter, and I'm not sure how comfortable it will be going winter camping in this thing. It's certainly not a "four season" tent, or even a three season one.
I bought it after reading a review in Backpacker magazine - that reviewer also hated "the banana position" inflicted by most hammocks, but he swore by the Hennessy hammock.
My estimate: probably great for solo backpacking, but likely not for survival situations.
The Treeboat looked very much like it would inflict a "banana position" on its occupants, but I've never tried one. I suppose because of the (rigid?) frame, you could fill it with padding to get a flat surface, but otherwise it looks like it would be fairly uncomfy after a while.
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"The mind is not a vessel to be filled but a fire to be kindled."
-Plutarch