From my experience, the best way for testing is a self-built app from Xcode (iOS) or PhoneGap build (Android) and testing on a real device in order to be sure that all widgets in your app work as well and they are looking fine on all different device screens.
In Xcode 11 (since you have to use it form 30. April in order to build the ios apps), you have a simulator and you can run the application to see how it looks on a real device (iPhone or iPad).
Mendix apps are ok for quik testing and to run the app on your device, however, I prefer testing on real devices in order to be sure that everything will work on real devices.
That is how I am working with Hybrid apps from the beginning.