For me, ergonomics is the most important factor of a reader. If I can't hold it comfortably and read comfortably, it doesn't matter that the screen is the best, the controller is the best, etc. If they had put the same form factor of the 600 on the 300, I'd have had a hard time indead. The bezel is too wide. I don't mind the larger space on the bottom, but for me, the screen should go all the way to the edge of the device. And there should be a forward/backward button on the side, preferably on either side (this would help if you're reading in bed, and turn from side to side
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Put those numbers on the bottom and replace them with a forward/backward button (or scroll button) and it would have been perfect.