It here are several things that are great about the glass chair mat. 
Pros 
no more dents from the wheels that make you feel stuck
At 14” thick, this mat doesn’t feel flimsy, shift or move once in place
It’s clear so it looks much better than plastic sitting on the carpet.
Con
It’s not ideal for all desks types.
My desk has file drawers on both sides with a narrow space between. I turned the glass so it fit between the opening because otherwise my chair would roll off the edge when sitting forward.
This mat would definitely work better for desks that have enough space for at least part of the glass to be underneath the desk without turning on an angle.