The Avanti Electra has regeneration, but not tied to the brake levers.
The handlebar unit (of similar size to a cycle computer) has one button for On/Off, and another button to cycle through Full/Econ/Regen.
Full is 200W out.
Econ is 100W out.
Regen is 50W into the battery.
In practice, there isn't much to be gained from regenerative braking on a bicycle. When you stop at an intersection it is usually pretty quick, and there is a limit to how much current you can pump back into the battery, so you won't recover most of the kinetic energy. The only time it makes sense is when you are descending a long hill, and even then it has problems. If you want to maximise energy recovery, you need to brake to keep your speed down to about 20km/h (increasing speed doesn't increase current into the battery). Personally I just accelerate to terminal velocity
If you don't brake and your speed increases above 44km/h (which it does on a hill near home) the controller turns off. You then need to brake to under 44km/h and press the On/Off button again. Moving your hand from the handlebar grip is probably not the best thing when heading down a hill at 50km/h.