I have an M-Edge Executive for my 505, and I couldn't be happier with it.
As I tend to shove it into things where the leather would be likely to get scuffed up, I spent a while looking for, well, a cover cover. What I found that works perfectly is a stretchy fabric cover (Book Sox knockoff) normally used to protect textbooks. When it's in place, it covers the unit with two layers of fabric, which will protect it from normal backpack wear. It was $1 at a discount store (I bought several in different colors). I'd also highly recommend the Lexol cleaning wipes and conditioning wipes if you get a leather case. I've been using Lexol products for ages, and they're the best thing that ever happened to leather.