I have, and use Calibre with LL instead and it still requires a lot of hand holding and manual grooming to get a clean library.
My big issue with Readarr is that it had a hard time fetching data for various popular and/or prolific authors. So if I wanted to fetch all the books for a particular author, there was a high likelihood it wouldn’t actually fetch the necessary book data to do so.
I prefer LazyLibrarian over Readarr but it still leaves a lot to be desired for end-user usability. One of the big issues with ebooks is that data is a mess, with each book having a billion different editions with spotty metadata support that makes it hard to tell what is what.
Goodreads seems like it was a decent source of data for these types of projects but they shut off new API access a couple years ago and legacy access can go away at any moment. Hardcover seems like a promising API alternative but not sure if anyone has started integrating with them yet. Manga and comics seem to be in a better state, with a more rabid fanbase maintaining data but still nowhere near what’s available for movies and tv.
Looks like it’s pretty easy to add assuming the instance adheres to the policy documented in https://github.com/aeharding/voyager/blob/main/src/features/auth/login/data/README.md
Edit: looks likes ToU and Privacy Policy needs to be added to https://vegantheoryclub.org/legal at the bare minimum. Probably worth pinging the instance owner to verify the criteria are met and submit a PR.