It's fully compatible with Calibre — that's how I run it myself: my books still live in a Calibre library, and BeePub just points at it and stays in sync (read-only; Calibre remains the source of truth). Same as calibre-web.
I've put a lot of work into CJK / Traditional Chinese support (including vertical text), and into manga EPUBs. There's also a native app built with Capacitor, currently on TestFlight (iOS). It also speaks OPDS and KOReader progress sync (kosync), so it plays nicely with e-ink readers.
If you're curious, play with it at https://demo.beepub.app (login: demo / demodemo — the data resets every 6 hours).
This is a project I dogfood every single day, so expect it to keep getting updates!
We also have a book gacha!