Had to replace the old mat as it was cracking in several places. Decided to buy a smaller one than the prior mat and without the lip. Never liked the look of the lip. This new mat turned out to look so much better and still is large enough for area that the chair needs to roll on. Really like it a lot. A good purchase.
Needed a new mat for very thin carpet squares glued over concrete. It works fine. Just enough of the little nubs to grip the carpet. My only issue is that if I sit still for a bit the chair sinks into the mat leaving small depressions. I am a smaller person and the chair is fairly lightweight. It sometimes take a bit to move the chair out of the depressions. I have only had the mat for about a week but the mat does seem to correct itself over a few hours. I am not sure if the results would be the same for a large or heavy person or a heavier chair.
I'm not very heavy (170lbs.) and my office chair has five casters so the weight is well distributed. However the chair still sinks into the surface when used on a medium pile rug making movement difficult.