CaptainRandy,

Actually, the clamp-on meters DO work, especially on brushless motors. There is never a constant flow of current through the wire between the ESC and motor on a brushless motor; it's always pulsing, which is what the clamp-on meters need.

They even work on brushed motors, to a point. As you get close to full throttle, the pulses to the motor get too close together for the meter to read. Other than that, it's surprisingly accurate.

I have a Whattmeter and a $10 Harbor Freight clamp-on meter. Haven't used the clamp-on in a while, but when I tested it, it was within 1/2 Amp of my Whattmeter.