This chair mat says for up to 3/4" carpet. I measured my carpet and it is less than that. The chair mat has dents in it from the chair and does not allow the chair to move freely while sitting in it. I will be replacing this mat.
It may protect the carpet but its thickness (or thinness) allows it to compress into the carpet and thus makes rolling the chair around tough - i.e. the chair casters get hung up in the divots . . . or maybe I'm just too fat!
I think my carpet is a medium pile and I have been using this chair mat for a couple of weeks and it has some pretty serious dimples where the wheels of the chair sit. I make sure the chair is not in exactly the same place on the mat as I believe that would make the dimples worse. I will keep an eye on it and update in the future.