Yeah, I think KOReader started out for Kindle first, and then added Kobo (and then other things - works on Android for one, and KOReader is typically what I use if I'm reading on my phone too). I just went with Kobos from the start because it seemed like there were fewer problems with Kobos w.r.t. getting locked in/out of things than with Kindles, though Kobos are harder to get hold of (outside of Canada, I suppose) than Kindles.