App Upgrade from TestFlight to AppStore

No, apps installed via TestFlight do not auto-update, and will not automatically convert to your App Store version

The user must explicitly download from the App Store.

Thank you. Once user install the app from AppStrore, will the data persist from TestFlight installed app? Like log-in information, etc... will persist in app from AppStore?

Following.

Hello, will there be an update prompt when you open the TestFlight internal test package after publishing to the appstore?

The application from the App Store will need to be downloaded/purchased and will replace past versions. Installs via TestFlight will not be auto-updated to the production version from the App Store.

I'm also in a similar position. For clarity, if I have a user using my app in the AppStore and he downloads the same app from Testflight, will that overwrite the AppStore app? Specifically will that mean my user loses the data he's already got in his app.

And then the same question applies the other way. If he's testing a new feature for me in Testflight, and then I release a newer version back to the AppStore, is there a way he can move between AppStore and Testflight versions without losing the data that's only stored on the phone?

Thanks

Yes, it may wipe out the data. Whenever you download the build from TestFlight over the App Store version application it’s asking for your agreement. Please see in screen shot image