The smooth nub design on the bottom is safer than the pointy nubs but they allow the mat to move around more on carpet requiring frequent repositioning.
When the product came rolled up I was fairly sure there would be an issue. After 5 minutes on the chair mat I had to bump the chair out of the sunken castor ruts. Way too thin for carpet applications ie. CHEAP
I purchased this for my office with a med. pile carpet. I am 200 lbs and I don't have any problem with divets or anything in it. I plan to order an additional one.
We ordered 2 which were received unpacked or bound together. One has a wrinkle that has not flattened out up until now. Staples should consider how to improve packaging to ship this item even if we receive free shipping.