Originally Posted by robko
Sideloads have been treated generally equally for a quite a while now. The only thing that really is different is that they won't sync between devices (this is a privacy issue since Kobo doesn't know what books you have that you haven't bought from them, so don't expect that anytime soon).
I'll let someone with experience with with O'Reily books comment on them because they seem to be a bit of a different beast to most.
Thank you very much for your answer !