I purchased this as a replacement. The size is exactly what I needed. Agree with some of the other comments about it very malleable which was a surprise. Very heavy and hard to put in place but great once situated. I think it is a bit pricey for a chair pad but so far so good so I can't complain. I've only had it for about a week now so don't know how durable it will be.
Hard to go wrong with a piece of plastic but it has made my office chair much more manageable. Just had new carpet and underlay installed and couldn't move my chair at all. Worth the money and fast service and delivery! Highly recommend!