Before I had a square 36"x48" mat. I wanted the lip so that I wouldn't roll off the front of the mat. However I found that the lip on this mat counts against the 48" and I was rolling off the back of the mat. Personal preference but I'd rather roll of the front and I returned it. Everything else was fine.
Don't waste your money on this chair mat. It curls up and then its hard to roll your chair over it. I have had to set heavy boxes on the corners to hold them down but it hasn't helped. By the time I realized that it was just not going to work no matter what I did and wanted to return it I had exceeded the time limit on returns.
The mat has dents in it from the chair and does not allow the chair to move freely while sitting in it. My carpet is less than 3/4" as stated in the description.