Here is an intriguing new device: Superpedestrian - The Copenhagen Wheel.
The red device on the rear wheel is a power supply.
My personal question is "How much does it help me in trying to go up a hill?" e.g. the hill to my house...from say NE 65th Street (Whole Foods) to Cloud City Coffee in Maple Leaf i.e. going up Roosevelt. Hardly a huge hill but enough to notice.
I am sure that a technologist would be able to figure out the "foot pounds" (or whatever) needed to cycle up a slope on my own effort and then how much supplementary power needed (and supplied, one hopes) by the Copenhagen Wheel to make me feel as if I was riding level. And that will be the measure in the real world of consumers: "perceived effort" with "riding level" the ideal.