I'm using on a medium pile carpet. Yes it dents and shifts a bit but they all do on medium carpet. I don't mind moving the mat back every few days. The material is a softer vinyl than my old one so I expect it won't break as readily. Dents are OK breaks are not. I wanted something inexpensive for a year or so until I move and this one will do OK.
My office chair sinks into the mat so the mat is not as firm as I expected. I bought it because of the shape and size that would fit into my office and desk.