On medium pile carpet the chair creates divots that are so deep it's hard to roll out of them. They aren't permanent divots - but at the time you are trying to roll out they still inhibit your motion. The mat also creeps forward but I haven't had one before so maybe they all do?
I shopped online for chair mats to protect my hardwood floor from my son's computer chair. This was the best price and it's a great value. Just what I needed and I was glad I hadn't paid for one of the higher priced choices.