I didn't know this existed until I saw it here on FreshChalk. I've used it a couple of times and it really relaxes my muscles and I'm not as sore the day after intense exercise. Yes it hurts when you first lay down on it, but after a couple of minutes, I find it comfortable and I can actually relax and drown out all the distractions around me.
It's not as scary as it looks! It is a bit painful at first to get used to the spikes on this mat, but if you have chronic back pain, this has been known to alleviate a lot of that. Just take a look at all the stellar Amazon reviews for this thing! After a long day of sitting weirdly, this thing loosens me right up. I always feel a lot less rigid the next day.