I am the opposite. I never understood why Sony placed the buttons below the screen rendering one-handed use extremely awkward. To use the low buttons you have to hold the reader by the bottom bezel which means there is a tendency for it to lean backwards and place a lot of stress on your thumb and hand. It was okay for landscape reading, but for portrait reading it gets an F from me in ergonomics. Holding a reader by the lower bezel also makes it more difficult to balance the reader on my fat belly.

The ergonomics of the K3 and K4 really outshine those of the Sony readers as far as one-handed operation. At least in my opinion they do.

EDIT: I've owned several Sony readers BTW, so I've used both Sony and Kindle extensively.