The TestFlight SDK for iOS has a submitFeedback method, so the user can give feedback from within the app and the feedback will show up on TestFlight for that specific build.
I cannot seem to find an equivalent method in the Android version of the SDK.
I know I can use the feedback e-mail address shown on the TestFlight page for the app build, but is there really no way to do this via the SDK?
TestFlight is dropping Android support, so this will probably not be fixed.
Ended up using HockeyApp instead, which supports iOS, Android and Windows Phone.