Is there anything wrong with stock Kobo firmware? My paperwhite is pretty dated and I was thinking of jumping ship.
It's a nicely hackable device though.
The reason was that Kobo has a sliding power button that allows you to turn it on/off. This is different that putting it to sleep. In order to save battery, I often turned it off instead of leaving in sleep mode. This may be a minor difference, but Kindles don't give you that choice and I prefer Kindle's simplicity, which allows you not to care about how your decission between off/sleep would affect the charge. People talk about this topic in forums https://www.mobileread.com/forums/showthread.php?t=146967
Good luck having a few thousand books on it.
Oh and of course old kernel, security bugs, spying, etc.