Helicopters and crop dusters are generally obvious to someone keeping their UAV in sight.
(medical) Helicopters and crop dusters arent usually trying to move undetected.
"We are trying to make the aircraft a little more stealthy," Barnhart said."
How fast can you land a drone at 400 AGL?
Descend too fast and you fly into your own prop wash and you are in freefall.
https://en.wikipedia.org/wiki/Vortex_ring_state
Descend too slow and someone flies into you faster than you had the ability to respond.