I gave it a 4 mainly because *I* may have bought the wrong one for my carpet. My carpet is thicker which I assume is what causes the mat to constantly shift up to 10 inches towards a filing cabinet. SInce the mat can't then shift any further left it creates a curve/bump which then causes my chair to move. I will give this one to the Goodwill and try another one specifically for thicker carpet.
I guess when you order cheap you get cheap. My chair still does not roll on this mat. It is actually worst than the carpet was. I need to return for a thicker mat. Not worth the money.