I've used CoolReader in the past, and recently suggested its sucesslr LxReader[0] to my partner, while I like the simplicity in MuPdf[1]. What do you think are the biggest advantages of Book Story? I might give it a try.
[0] https://gitlab.com/coolreader-ng/lxreader
[1] https://f-droid.org/en/packages/com.artifex.mupdf.viewer.app...