I figure, even with the bumper guard, my dog would have trashed the seal around the bottom of the hatch. I just lay the towel over the bumper and the seal when my dog gets in and out, and it looks pretty good. No damage I can see.
I did let my dog get in and out once without a towel, and I could see scratches in the bumper.
A better option, in my opinion, would be some 3M clear bra for the back bumper. Way better looking than a black rubber mat.