Yes, 五线谱 is free to download, however it contains in-app purchases or subscription offerings.
Not enough reviews to make a reliable assessment. The app needs more user feedback.
五线谱 has several in-app purchases/subscriptions, the average in-app price is €9.99.
To get estimated revenue of 五线谱 app and other AppStore insights you can sign up to AppTail Mobile Analytics Platform.