I use the chair mat on my painted concrete floor because the rollers on the computer chair wear away the paint on the floor. The only bad thing about the chair mat is that the spikes on the bottom side wear down after a while due to the rollers on the computer chair.
I wish I could say this mat is perfect but I was disappointed to find that it was bendable enough to be rolled and put into a box for shipping. I expected it to be too rigid for that. It's a nice mat but not thick enough or rigid enough for plush carpet with a thick pad underneath. It would probably be best on low pile carpet with a thinner pad.