Well from my experience
The main problem with my Kobo mini is that the firmware is annoying. It tries to get you to use their store. I don't want a store connected to my device. I want to get files, for example by buying them DRM-free (which I've done several times already despite of problem 2) or getting them from a free source.
Problem 2 is that it's rather small and really bad at pre-formated files like PDF or plain text.
Biting the hand that feeds IT
