We saw these at NAMM this year and just couldn't resist stocking them even though it wasn't a banjo specific accessory.
Saying that - I use mine all of the time to practice banjo.
- I can play along with a my iPhone's metronome app and amplify it so I can hear it.
- I play along with tunes from my iPhone / iPad / laptop.
- I can transcribe solos easier from my iPhone / iPad because it is now louder and clearer.
Then I can listen to music clearly anywhere my iPhone / iPad is! And this is an FM radio as well!
There are other Bluetooth mini speaker units out there - but this is the best one I have heard yet!