I actually made a high-pitched excited noise when I saw this on the list of available plugins. I love ABS and have been syncing some of my audiobook metadata manually, and this is going to make everything much easier!
I've only used the Narrator and Duration syncing so far, so I can't comment on any other aspects, but I do have feedback about syncing the narrators: my narrator column in Calibre is "ampersand separated text" since it's names, but the plugin separates the names with a comma. It seems counterintuitive, taking Calibre's default treatment of names into account.
Also, I have an enhancement request.
I have two distinct libraries—necessary, as they're not something that can be handled gracefully using virtual libraries—and I'd like to be able to sync both. My ABS has matching separate libraries, too, with separate IDs, so I think it'd be a pretty easy thing; it should only require the plugin to save settings on a per-Calibre-library basis, which I'm pretty sure is doable. Thoughts?
Anyway, thanks so much for making the plugin in the first place!