Although it does dent while you're in the chair and takes a bit of effort to move if you've been sitting a while the dents don't seem to last. I picked up 15 in-store because of other reviews saying they had been rolled. Very pleased with this purchase so far.
I have an L-Shaped desk and this mat fits perfectly. It seems sturdy and robust. I really like it...as much as a human can possibly like a chair mat...
I just wish they lasted longer. My chair mats tend to last about 3-4 years and then they are cracking and I need a new mat. But it's better than having your carpeting (or your wood floor) ruined. Just be sure to get the mat made for your type of flooring.