That beep was added on our second version we released.
We noticed that the control signal goes away VERY quickly when something isn't right so we warn you when it is below 85% for more than a couple of seconds. This is also why we implemented the direction indicator so you can track the aircraft by pointing your remote towards it to maximize the signal.
For mapping of hilly areas, try to start as high as you can so the overlap is calculated for the high terrain and the terrain below will just have even more overlap.
We know that the app eats battery pretty quickly. There are a lot of vanity features in there that we might add a low update rate version to conserve battery. Once you are comfortable using the map for updates you can also turn off the video preview. It uses software decoding that is an absolute battery hog.
We are already looking at sharing missions across devices. Think swarms...