The 2 applications we have : Metafields Editor and Metafields Pro require certain permissions to be granted in order to access the metafields.
The apps can access metafields related to Products, Customers,Collections, Orders, Blogs and Pages. Just by granting permissions to view such data does not mean the apps would access the data without your explicit actions.
The app would download data as described here when performing various imports/exports. The data collected is only used to perform the necessary actions on the app. Your customers or orders data would never be shared outside the apps.