It will scratch easily if you place the item on something like a brick patio wall.How possible is it that the aluminum back side of the iPad Air to be scratched? So this raises the question of if its better to get a smart cover rather than a smart case?
Bear in mind that the iPad 2 had a metal hinge. The new Smart Covers have an all polyurethane external. OP, I wouldn't worry about it.
I think what Richardgm meant was that the back of his iPad was scratched but the cover did its job protecting the screen. I don't think he meant the cover scratched the iPad.