The only design change I would make (after having used the customizer - lovely bit of work, that) would be to make the 505 a little less slippery. Sometimes the case is a bit bulky to hold, so I like holding just the reader while reading, and if you are holding the reader over your head while lying on your back, occasionally I lose my grip and get bonked in the nose.
I have considered applying thin rubbery strips to the sides and back for grip, but haven't found any that would not be ugly when placed on my very pretty reader.
Overall, I like the look, the buttons work as I want since I used the customizer, and the page turn speed is fast enough. And mine is BLUE!!
Mare