Google music is that it seems to lock the tracks away in a database so you cannot use them on other devices (eg a traditional mp3 player).
that’s completely the opposite of what you can do.
You can get your music on any device:
Android device – use Google Music to sync & Play
PC via Browser – use play.google.com to access your music from where you can stream play, download the album as mp3 to play locally or move to a device or even Share it with a mate. And you can do that on any internet device, any time.
It’s far more versatile than Amazon or iTunes.
You can use Music Manager to download your entire library if you want to, or just tunes you want.
https://support.google.com/googleplay/answer/1229970?hl=en-GB