The grip points are bevelled and therefore do not maintain adequate grip on the floor. As the chair moves around so does the mat. Also the plastic used could be a bit thicker. Returned this mat and bought a different brand which works better.
this chair mat smells awfull even after one night with an open window you can smell the chemicals coming out of that thing. Most likely it´s made out of PVC containing phthalate plasticizers which are unhealthy. I will return it...