This sounds technically more complicated than just measuring the amp draw. I think the Monaco is just what Roelf did with a fancier box - and actually its box is probably the most expensive part.
its more complicated conceptually but its simpler from an application perspective. My point is that Roelof is doing it the right way. In the long run an ammeter accounts for wear and changes in the mechanics.
if a motor spins at 1000 rpm and draws 1 amp and that means 1nm of torque at the motor and a gear ratio that results in 10nm when the motor spins 500 rpm it delivers potentially half the torque.
if you use a torque transducer to measure the torque at each rpm (or an ammeter) you can do it once to calibrate the tester. The processor in the tester takes the rpm and spits out the scaled torque based on the calibration that was done at the factory.
Roelof is very smart and what he made is just as clever. My only point is that its probably superior than an off the shelf solution. It really doesnt matter. Its just talk but Roelof has helped me out in the past and i was commenting on how i think he is doing it correct.