I think your success with these apps depends heavily on your country. I always hear good things about Libby in the US but the equivalent here in the UK I think is absolute dog shit.
The selection is woefully small not even including really popular books like say lord of the rings for example, you can request books are added but they have a finite amount of books they can add in a month and of all the things I requested they never added any of them.
On top of that often I would have to join a virtual queue because someone already "checked out " the audio book I wanted to listen to and so you have to wait for them to finish. Often as well they wouldn’t “return” it when they had finished so I’d have to wait until the standard amount of time was up and the system forced them to return it before I was able to listen to it.
It cost a tenner a month to get access to this service but in the state it was in last I tried it I wouldn’t even say it was worth that.