Three stars because none of Barnes and Noble apps allow purchasing direct within NOOKAudiobooks , I'm sure there's a reason, but it annoys me.
As far as NOOKAudiobooks 's functionality, I read the reviews saying it didn't work, but it worked fine for me on an iPhone 6S, and iPad Air. I listened to Hornfischer's "Last Stand of the Tin Can Sailors" all the way to Dallas and back.
There was one flaw, for the first 20 minutes the playback stopped at each new track, requiring me to hit play again. It's possible it was something on my phone, or in my audio system connection, as I could find no other mention of it, and it actually went away after a bit and has played flawlessly since.