This is a "toy" with a single reinforced carbon fiber main-rotor blade 5 feet in diameter, which is flown pretty much exclusively by people like this for the pu

This is a "toy" with a single reinforced carbon fiber main-rotor blade 5 feet in diameter, which is flown pretty much exclusively by people like this for the purpose of pulling very physics-defying stunts, flipping and turning and changing direction faster than a dragonfly could, two or three maneuvers a second in directions that are not aerodynamically favored. It is designed to accelerate very fast, and that means spinning its rotors many times faster than is necessary to hold it up in the air, so it can bleed off that velocity in a 100ms maneuver. These are not a new innovation - they use dirty 'nitro' (liquid fuel) engines, and have been around for decades. They are inherently dangerous, adult toys, and anyone flying them without binoculars on assumes a certain degree of risk. Even so: it requires a very unlucky shot to kill a person with a 700-class helicopter, and I find the concept that it 'sliced off the top of his head' sensationalist garbage. Tens or hundreds of people out of the tens of thousands operating these machines end up with deep scratches or partially amputated fingers (you can see them on Youtube), but the time since the last fatal accident is about a decade. These are completely unlike the safety issues posed by various categories of planes and multirotors, or by remote camera-driven operation of those aircraft. There are very real advantages to a society in which these things are legal, and with a lot of the useful ones, I would be comfortable flying one into my face to demonstrate; The larger examples that can fly heavy DSLRs, perhaps aim for a limb. It's more like someone demonstrating their finesse with a hobby of medieval flail weapons paid $1000 to buy an authentic one, put on shows entertaining people with it for a few years, and then in a slip-up gored themselves in the back of the neck. The risk and speed is literally the draw with these things.