There should be a good termination of th program so Ican easily switch to DJI GO for picture Review
The Android Operating system is responsible for terminating applications once the user closed it. It is an operating system process that determines how and when what will be terminated when you close an android application.
Putting a "close" button or "terminate" button inside of Drone Harmony would wrongfully create the impression that Drone Harmony can control how the termination process of the application will be handled. But this is not the case and thus this is also the reason that almost no Android application offers a "close" button.