[taming]

I think they are saying that when a user cobbles together an epub or gets it from non-kobo sources and then sideloads it onto the device, where it will go through either the Adobe or the Kobo renderer, they cannot guarantee that the fonts will perform as well as a book that has been coded to spec.

I have yet to see a problem with epubs purchased from any legitimate epub retailer, other than those problems that are evident in kobo-purchased books ,too. If I buy an epub from Kobo, it is no better than the same book purchased from Sony, or Google, or B&N. All of these may very well be better than a book downloaded from torrent sites, manipulated in calibre, created by someone for private use, etc.