I've tried several and they all have their place. THe one shown in the picture, I have two of them and used to lie on both for deep, long relaxation sessions, or just to go back to sleep if I woke up too early. Got a little addicted to them almost and realized after a while that I was waking up just to get on the mats and fall asleep again. It got a little silly.
Anyway, the Shakti Mat is nice for lying on and standing on. Better for lying on is one that is made of plastic and inflatable, comes closer to the body and is more "ouch" in the beginning but more calming in the long run. I have one called "The swedish bed of nails" and it's made of hard plastic and the nails are fewer (600 instead of 6000) and longer. This one really hurts the first couple of times but gives a much deeper, massage like effect.