I have never heard of 'dynamo regen'. It sounds like an answer to a question no one asked. Most e-batteries have taps for 5V power to charge cell phones, or the display unit has USB jacks, but either way you get the power for your electronics right from the main battery. Using energy from the battery to run the motor as a generator ... I don't even think it's possible. A motor can either be using power and providing motive force OR it is converting motive force back into power (at greatly reduced efficiency) it cannot be charging a battery or running electronics while simultaneously providing motive force. No. Just no. Unless there is a second dynamo on board, the only time power can be recovered is during coastdowns. It is only e-bike customers that want regen, because they think it is magic. Perpetual energy. Free energy. There is no free lunch.
I don't have exact numbers, but think of regen kind of like this: if it takes 100W of energy to go up a hill, going down that same hill with regen on will get you 10W back into your battery. So you never recover all the energy you used. Not even a decent fraction, just 10%. Maybe enough to keep your electronics on but nothing usable to extend range. So few manufacturers offer it. Ebikes.ca offer it with the proviso that it works in some situations. The rest are playing on the need for most people to think they are getting away with something. If you want to get away with something: COAST every chance you get. The world record range champions use power in bursts and coast in between. Staying off the brakes as much as possible is what extends range. You can't do that in town (not safely) and regen can keep you from using up brake pads as fast but I can't really remember the last time I put new brake pads on and I don't have regen. So ... more than you needed to know but that's how I roll. No regen holding back the flow of information ... FWIW ...