Interface seems like it's for mobile only.
A lightbulb icon looks like it would be a dark mode switch but no, it opens up a FAQ.
Settings make it too easy to set a background without changing the text color (The options aren't next to each other, and the default custom color scheme is black on black. What would be really nice is a dropdown of a few color schemes on the scale of light and dark, with the option to make a custom scheme.)
In the "Website" reading mode, a cover image was displayed absolutely bonkers huge, filling the width of the screen even tho it's 324x500 (small, so it was really pixely, and tall, meaning it didn't even fit on the screen because the size was based solely on the width).
Finally, nail in the coffin, "The ebook is incomplete and can unfortunately not be opened." (even tho it did open it at first, and showed at least the table of contents and part of the first chapter)