First this is a good quality chair mat. It's flexible (not stiff) and the cleats don't dig through the carpet and mar the floor like the old-style sharp cleats do. But...it won't stay in place. I am using it exactly as designed - on flat-pile carpet - and it is constantly sliding. I have to re-adjust it at least once per day if not more. I guess if you sat at your desk all day without ever getting up this wouldn't be an issue but most of us don't do that.
The mat works exactly as intended. I am using it with a medium pile carpet. I am on my third mat they last about a year and then they crack. Up until the point that they crack they are a great product.