For XC flights you need to hear a vario with a sound of good-quality. You’ll appreciate an actual height, a flight speed and a compass – these are basic functions. You can fly without them also and don’t have to take any devices for a flight with you but that’s not a good idea. Nevertheless, in practice you won’t use a computation of glide ratio to another turn points in a new flying area. And the navigation with a dart – if you’ll define at home in advance your target points or some points in case of need/emergency, then it’s fine. Man proposes, life disposes. So at the end, I choose the easiest and energetic undemanding devices. The good trick is to have the same charger for a camera or you can take out batteries and use them in a headlamp. On the market are a lot of devices and possible combinations. I use a basic Brauninger and the easiest black-and-white GPS to don’t feel bad if I’ll lose it somewhere. I don’t use a GPS on my phone for flying because I want to save the most of the battery for listening to music and audio books. But it really depends what everyone prefers.