At EcoSpeed we don’t do regenerative braking for a very simple reason. What works on electric cars doesn’t necessarily work on electric bikes. All electric cars have regen braking which recovers a small amount of energy from momentum during braking. Most estimates of the amount are in the 5% to 10% range. Electric bikes are light and travel at low speeds. As a result they have very little momentum so less energy is available to be potentially recovered. To recover that small amount of energy, regenerative braking systems either require that the motor be continuously engaged or that clutches be used to engage the motor when regen braking is needed.
No one, including EcoSpeed, uses clutches because of the cost and complexity involved. A continuously engaged motor means that there is always a drag caused by the motor’s cogging torque. That doesn’t matter to a car since the motor is going to be in use almost all the time. Bicyclists, on the other hand, have been known to pedal. That means you are using your muscle power to overcome motor drag whenever you are pedaling without the motor turned on. The loss from that drag can easily exceed the power you get back from regen. In other words, on a bike, regen braking can actually cause a net loss of energy! If you want the gory details look here (.pdf file of complete article).