It's really something that my e-reader has better and more usable scrollbars than most desktop interfaces (Windows, MacOS, and Gnome). :/
The scrollbar is thin, but the grabbable region is large (kind of like the default in KDE), and easy to manipulate directly with your finger. This is actually better than #iOS' implementation, and many #Android apps.
I haven't tried KOReader on it yet, since I also want to use Overdrive books.
My only gripe is that it's surprisingly difficult/clunky to take screenshots without installing third-party software, and the "handles" for changing the highlighting points aren't offset enough. They look offset, but when you start moving them, the insertion cursor is basically right next to your finger, instead of above or below it (like on the Kindle), and it makes it very difficult to see where exactly you're extending the highlight to, so if you're #ADHD / #CDO like me and want the highlight to stop on the word and NOT include the space/punctuation afterward, you get kinda frustrated. XD
lol I'm such a self-caricature at times. XD
So, Kindle handles highlighting a bit more intuitively, but AMZN is hella evil, so whatevs. XD
R.L. Dane 
🍵 
Dave