Most quad copter blades won’t go through your skull:

https://abcnews.go.com/US/minute-mechanical-error-led-teens-...

Proper helicopters also require a complicated control linkage on the main rotor and a separate tail rotor. Quad copters (and other multi-blade devices) only need to modulate power to the rotors for control.

I would never ride a quad copter, but they’re better for unmanned use.