As others have said – nope. You can get a cheap enough Kindle without ads (and yes, it is absurd that there's an ad-version in the first place), and sideloading is a piece of piss. Either use Calibre or set up a Kindle email address. I mostly do the latter these days. The only downside (and the main upside to using KoReader, I would think) is that you don't get the full range of typography options sending over EPUBs this way – you would have to do a KFX conversation first (again possible with Calibre, but a bit of faff).