The two chair mats we bought work very well at our two work stations: my home office and my wife's sewing machine cabinet. They enable us to move our older office chairs between desks and work tables - over wall-to-wall carpet.
Rather than going for a more expensive mat I went with this one. After about 3 days of work I have indentations where the chair sits most of the time. Now it seems to always gravitate to those indentations which eventually will probably go right through the plastic. Don't recommend.
I don't think you can find a better priced carpet mat anywhere. The quality is comparable to the price. On thick carpet the mat sinks and chair traces are easily visible.