The thing I find the most valuable on KOReader is something I haven't seen mentioned yet: the book map[0]

It shows you chapter and section divisions in a single screen, along with black bars to show you which pages and chapters you've spent a lot of time on. I use this very often to jump back to pages or chapters, or look at which parts confused me. It also visualizes where bookmarks and notes are. When you want to see a segment in more detail, you click there and it brings you to a 6-page zoomed-in view.

Let alone being more useful than the Kindle or Kobo UX, it's more useful than the book UX.

[0] https://www.tc3.dev/posts/pocketbook-era-with-koreader/IMG_6...