Who has one? Is it worth the money? Would it be a good thing for someone who needs to be able to sleep flat and not have my shoulders curl inward and my hips flex while the "heavy parts" sink in?

Therma-Rest on the floor or very firm futon are the other alternatives, but they kind of make my sacrum sore before morning comes, so I'm wondering if there's something more ... if it were vehicle suspension one would say "compliant," something that's soft when you want soft and firm when you want firm. Someday I might even be able to sleep on my side again.