I've got the iPad Pro 12.9 and the keyboard portfolio which makes the back flat (and generally non-slip). On my previous iPad pro (the 10.5" one) the 3rd party

I've got the iPad Pro 12.9 and the keyboard portfolio which makes the back flat (and generally non-slip). On my previous iPad pro (the 10.5" one) the 3rd party case did the same thing. That said, the bump in cost from an iPad Air 2020 and an iPad Pro makes the Pro a lot less attractive. You get wide angle, face id, and larger "top end" in storage.