Chair mat is too thin to be effective. Leaving chair on the mat overnight resulted in dimples where the chair's wheels were. Might be fine for low pile office-type carpeting but I'm using in home office with household carpet and it just sinks down too much. I cut 2 ply cardboard to same size as mat to place underneath and that seems to help but it's not very attractive.
I have an odd shaped desk. This worked perfectly with a small modification made with some strong scissors. Great to buy from the store and get it set at my desk the same day.