here's the breakdown, been sleeping on one for 7 years, actually two cause I had em replace my original last year.
1. If you keep your house above 74 degrees farenh. don't buy one... I moved to south florida from ohio, typical Ohio house temps are 67 to 72, here in FL it's 75 to 79... once the temp goes over 75 the thing becomes a freakin sponge and it's no better for your back than any crappy bed.
2. They are the absolute worse bed for sex. You knees sink in, her as sinks in, and there is absolutely no bounce like you get from a normal mattress.
3. Despite what they say, if you have an active sex life and you move houses/apts it will wear out and you will get a sag in the middle from the sex and folding when you move. I had to have mine replaced because of this. I fuck alot
If you have a cool house, don't mind the lower quality sex surface, it's definitely worth it, plus they do honor their warranty to my great surprise. Don't be surprised if it loses it's firmness after the first year though.