Good day, the app is great, a few things to add, would be in my opinion.
Folders for books, so in the main menu you can open the book collection folder, as some books have several tomes.
One more thing too, when you burn the firmware without having any books, the settings page is invisible, basically the swipe up doesn't show anything, unless a book is added in books folder.
But over all it is one of the best epub readers on the M5Paper S3. <3