Several years ago I met a Japanese gentleman who had invented something similar - only his had 4 engines. I believe any two could keep the machine airborne, as like this one, it had no blade pitch control.
This one would not survive an engine failure, as lift is controlled strictly by RPM - if the engine fails, the blades will stop pretty quickly, and you couldn't pull pitch to stop the rate of descent.
Neat idea, but don't go higher than you'd like to fall (and have the engine land on top of you, to boot).