Don't understand how people can read book on an LCD tablet display, e-ink is better in every respect. Just no way you can read on a tablet in anything like normal daylight, either the backlights are not strong enough, or the reflective surface means you spend most of the time staring at your own face (not pleasant, in my case...).
If I'm really desparate for a bit of late-night lit without distubing the Mrs. I can just about tolerate the iPad with white-on-black text on minimum brightness for 30 mins or so, but Kindle Keyboard with a little clip on light for blackout scenarios does me great.
Also 10 hours might be good for tablet, but e-ink battery is measured in days, not hours. I use my Kindle every day but only charge once a month.
Incidentally, e-pub, mobi, whatever. Calibre renders the original document format completely moot as it can convert from anything to anything seamlessly and allegedly can remove DRM in the process, but I'm sure I wouldn't know anything about that...