So, I won’t get into the whole privacy discussion, but I’ll say that for myself it provides the protection I feel I need. But if you go to Duck.ai, and ask the following, it will list some details on your concern. It is a good place to start to understand MicroG more.
“how does microg protect when a google account configured”
As for the Audio discussion, here is a topic I opened earlier in the beta. This was started based on the discussions that revolve around alternative stores, and purchasing options. It may provide you an alternative. USB Audio Player Pro was the app I was looking to buy, after talking to the app’s developer.