I've been using it for a few months now and I think it is great. I can't compare it to Goodreads and others because I have not used them, but it is pretty straight forward to add a book, give a rating and write a review. I like the UI a lot too.

The only problems I have with it is that the API they use is not very good for adding books in my native language and that backup is manual and I don't know if it has integration with Android's automatic backup.

Also, it would be nice to be able to write multiple reviews for the same book, it would be cool to see how much my vision and opinion of a particular title changed over time. I should probably suggest this feature on their github.