That is exactly how I ran some of the tube furnace experiments. Every time the thermostatic heater kicks in the data logger records the on-time and the current. Although the current was notionally constant, some of the heater inputs were so brief that they beat the 'rise time' of the heater coils, so it was always measured and timed
Comparison of test and control is relatively easy then, once you establish the complete calibration for any given furnace.
I think It is a clever and relatively easy way to wrap around the complexities of calorimetry, for obtaining a clear cut and relatively quick answer. It probably won’t convince any purist, but a reduction of the energy bill is always convincing for engineers and investors.