Initially very good, after 20 minutes no longer ...

The app does what it should in the first moment, they are the connected device (in my case the Fire TV Stick) as Air Play loudspeaker on the network. My iTunes has the Fire TV Stick or this app recognized directly as AirPlay device, the music playback worked perfectly.
However, if you have multiple AirPlay devices and connects the meantime with iTunes, iTunes gets confused when it comes to stream the music back to the Fire TV Stick. I do not know whether the at iTunes (latest version on a Late 2014 iMac) is, or whether the app actually not quite work. Anyway:
To date, unfortunately, only two stars, if there still should do what has the potential to make the app five stars fully.