Audiobookshelf doesn’t support OPDS, and if that’s your use case, you’re probably better off with Kavita.

I’m okay with it because I can fire up the web browser on my pocketbook ereader and download the books. It’s clunky but it works well enough for me.

I haven’t implemented it yet, but audiobookshelf does support sending ebooks to devices via email. I just haven’t bothered to get a mail server up and running for it.