(dev here) Completely understand the concern. This uses an embedded Google File picker to allow you to select what Sheets to allow access to. Until you do that, the extension doesn't have r/w access. The integration with Google (OAuth) has been verified and gone through their review process to only request/use minimal perms for the extension to function as expected.
https://www.addtosheets.com/blog/how-to-save-data-to-google-...