Does TestFlight erase production version data?

I have an expensive app ($300) that my users depend on for their daily work. I would like to have some of those users Flight Test an update I have prepared. But I don't want to erase the private data that the current production version has stored for each of them. Can they safely use TestFlight to load the beta version of my app without losing the data currently associated with the production version? And can they easily dump the beta version and return to the production version without losing that data? I know that if they uninstall the production version first, the private data store and settings they had developed on the production version will be lost. So I want to ensure that my testers will be able to test the beta version the same as if they had updated from the app store, in which case the private data for the app would be preserved.