I have two cases for my Aura that I purchased from eBay. One is
this one and the other is similar but with a thinner cover. I can't find a link for the one with the thinner cover, unfortunately. I don't own the official sleep cover, so I can't compare the magnet strengths to that one, but between the cases that I do have, I do find the thinner one easier to open. The magnets don't seem to be as strong as the case with the thicker cover (the one I linked to) and there is a bit more of a lip.
These cases seem kind of similar to my thinner case. There is no stitching on the cover and the metal piece is shorter, but I can't say for certain if it's like mine or not.