While I wait for feedback from DJI customer service concerning my defective 620S ESC I thought that I would do some testing to see if the 620S is indeed a true sinusoidally commutated motor controller. Here is a short video demonstrating that it indeed is a true sinusoidal controller that should be measurably more efficient than most, if not all, other multi-rotor BLDC motor controllers that use trapezoidal or any other commutation, at least in the consumer RC world.
Update 3-16-2015 for clarification:
I would like to point out that once started the commutation of the BLDC motor, by necessity, operates in a closed feedback loop mode. (sensor or sensorless feedback) The PID speed control portion of the motor controller (ESC) may, or may not, operate in an open loop mode. However, in a multi rotor helicopter application the relative speed of the motors, which directly affects the attitude and positional changes of the aircraft, ultimately form an indirect closed feedback loop to the Inertial Management control portion of the flight controller. Remember that a multi rotor helicopter is inherently unstable and could not fly, or be controllable, without operating in a closed feedback loop mode.
For some really good background information see Microchip Application Notes:
For comparison here is a snapshot of a DJI Phantom motor being commutated. The voltage wave is more of a triangularly shaped waveform than either trapezoidal or sinusoidal and has several discontinuities,. At any rate is is significantly dirtier than the DJI 620S ESC: