what? nobody mentioning Koreader? Light years ahead of whatever Nickel reader comes with the thing.
Sorry, I never used any custom firmware on our Kobos. You see, I keep them offline, so I'd care less about security vulnerabilities in them (plus if they go online, its via guest network). Also, I am very content with the software on our Kobo readers (Aura One and Aura Two). I do use Calibre + USB sometimes. What am I missing out on?
Supposedly lots of other features as well , but simply supporting djvu is so huge for me, I can't imagine bothering with nickel.