The chair mat is usable. It does get these indentations but the plastic does come back. For me it is not that much of a problem and I am 200lbs. For the price it is a good purchase for me considering that a larger glass mat would have ru over $200.00.
The wheels on the office chair forms depressions in the mat almost immediately. This makes it very hard to move around. A heaver / stiffer mat would be better.