You have to do a bit of research to make sure you get the right one for you. They have different elasticity levels, a lot of stores will have "sales" where they sell them off, but they are actually only saling the "hard" ones. Do the research first, make sure you are aware of the level of softness vs support you require before you buy one - don't get them blind.
That being said, my biggest complaint about them is I found it incredibly hot. I know a lot of people on here are complaining about coldness, I had the opposite problem, and I'm one of those people that is always cold! The material in the mattress doesn't breathe as well as a normal fabric matress, and laying in one place all night I would get really hot and sweaty (and I never sweat in my sleep.) I was waking up more every night having to move to find a cooler spot on the mattress. Most stores that sell the mattresses can also sell you covers that wick away the moisture, get that, but also get a traditional thick pillowed mattress pad on top of it to get some air flow between you and the surface of the mattress.