If they indeed do emit scalar waves, then we should see an EM signal in the collector when the two scalar waves interact be destructive interference, and yeild an EM wave. Constructive interference would produce a larger scalar, with no EM coupling to the conventional coil. This should suggest a great many ways to isolate an energy source from back EMF and other effects. It's a lot more fun than chasing rolling balls in my opinion, but its a heck of a lot more dangerous too. I shall try to generate schematics for the super-regenerative detector over this weekend.
Calorimetry seems be the safe method to see the excess energy if there is any.
These circuits can be considered as semi controlled experiments that we only be content to observe what they produce carefully but not try to optimize the effect. Expensive instruments like spectrum analysers and high bandwidth scopes and good RF signal generators will be very useful to see and understand what is going on on these coils. Power extracting should not be the first goal of these circuits. Circuits gives always unexpected outputs and puzzle us keep interest on it. This for sure.