I went shopping for a chair mat to supplement the one I already had in my office. Staples had a variety of mats in different price ranges and qualities to choose from. all nicely displayed so that I could compare them and pick one that would work and be compatible with my underlying carpet. Not damaging the pile on the existing carpet was important to me as the mat was to be used in the office of my home rather than in a commercial setting. The sales person was particularly helpful in bringing up points that I wouldn't hsve thought of.
I've lost count of how many of these I've bought over the years. The "lifetime warranty" implies they last a lifetime but I get only about 2 years of use before they start cracking and breaking.
I replaced my nasty old chair mat today and with this new mat my chair glides like a hot knife through butter. No more getting stuck at my desk (at least my chair that is).