I do use it. I found it because I was trying to get away from goodreads and searched for federated alternatives. I also am on storygraph and was on one called Orkut (or something like that).
There is an app, but its mostly just a web view as far as I can tell. I do find the interface a little early web compared to storygraph.
Fwiw the feature I care about most with these services is book tracking, and bookwyrm solves that. Sharing books with my network would be nice but I haven't managed to pull people from goodreads. I'm still gently attempting, but its difficult