We have the chair mat under our computer chair which has fixed feet not casters. It works well with our kind of chair ;not sure how it would perform beneath casters.
In spite of being designed for carpet it still "creeps" on the carpet and doesn't stay put. It is too soft and pliable so the chair doesn't roll well and I have a high-end chair. This product needs to be thicker sturdier to work on carpet.
I purchased this chair mat because I just carpeted my office it was very inexpensive and it was the only one small enough to serve the purpose but not take up loads of room. It stays put very nicely and keeps my carpet from getting marred. It makes it easy to move my chair around since my office is very small and I usually just roll over to the fax or printer I enjoy shopping at staples for my office needs because the site is so easy the prices are reasonable I get free next day shipping and they have almost every thing I need.
This mat fits perfectly in my L-shaped workspace but my chair tends to "sink in" to the carpet and make it kind of hard to roll around. I've had it for about a month now and it has not cracked or showed any signs of wear. Stays put very well.