The feature works for both Prime Music and Music Unlimited users, and you can turn it off if you don't like the thought of the app waiting for your voice commands.

No, this isn't likely to make you jump from Spotify or Apple Music. However, it does create the kind of harmony that Amazon likely wants if its music services are going to grow. If you have an Echo or another Alexa-powered device, you'll get a consistent experience when you're switching to your phone.