The Grvity plane concept is similar to the ocean gliders that have been used to collect ocean data for some time now. It does the same thing, but instead of using air for aqautic boyancy it uses helium for atmospheric boyancy.
Once it’s at altitude it can glide down on wings, collecting some energy from small vawts who’s energy is stored in the form of compressed energy. The speed it develops generates lift so the plane can cover over 500 miles without fuel, only based on the energy to decompress and compress the helium.
The plane is safe because it doubles as an air ship, it floats in the air anyway. It could use a propellor in our humble opinion, or it may float off..