I have belkin folio, poetic slimline, extreme Mac folio which non scratched the corners. Just be slow and easy with them and you shouldn't have any problems.
Thanks weisjt. See the link below. This case has a hook the clips on to the side of the ipad -- doesn't seem the ones you've listed have that. Any concern?
I have the leather like folio sold at Best Buy made by Rocketfish. No scratches so far. But I'd like to find a folio that is easier to take the iPad mini in and out of.