I think it's pretty common though, for example buying a "key" separately from the main app. https://play.google.com/store/apps/details?id=com.keramidas.Titanium

I think it's pretty common though, for example buying a "key" separately from the main app. https://play.google.com/store/apps/details?id=com.keramidas.TitaniumBackupPro https://play.google.com/store/apps/details?id=com.keramidas....