Advantages over fixed wing and multi-rotor:
Specifications
Advanced
development status
HALE vs Satellite
HALE vs Google Loon
HALE vs Google Titan/Facebook Aquila
Specifications
Safety
Drifts down slowly
in case of system failure
Harmless rotors
rotors are frangible and cannot injure
Redundancy
upper and lower balloons are independent
Scales Better
2x footprint=8x payload/endurance
vs
4x for airplane
Endurance
Large slow rotor
40% more energy efficient
than small fast propellers