Cool idea, but pretty expensive. Might be worth the price if you could run linux on it, but I suppose that would drain the battery pretty quickly; I'm not sure how well the Linux TTY is optimized for e-ink. Either way, only being able to type on Qwerty and Japanese Kana input is pretty limiting considering that the main feature is being able to type stuff.
Too bad it doesn't seem to have any kind of encryption option.