It's all a gimmick to separate fools from their money. The amount of capture varies drastically depending on the weight of the moving mass, terrain, and most importantly rider dedication to squeeze out the max capture rate. 99.9% of ebike riders wouldn't benefit from regen at all, and of that 99.9% of riders, only 1% would be willing to pay for the ability. The money is much better spent on owning high-quality, high-capacity batteries in the 1st place... but those don't come on production ebikes. Why? Because the manufacturers want you to burn through the packs and buy more. The bikes are sold with packs so small they require full charge and full depletion to get anywhere close to the advertised range. Even the chargers they provide are designed to get the minimum number of recharge cycles out of the batteries. Owning a battery big enough that you can ride further than you want in a day on only 65% of the pack's capacity will triple the life of the battery. Extending the number of recharge cycles from approx. 400 to over 1200. But ya need a great charger to manage the battery like that... the Grin Satiator is another expense people don't want to pay. Another benefit of a big battery is that you can charge at higher amperage with faster charge times without stressing the individual cells. The amount of power you can capture from regen hubs is negligible in comparison and completely unnecessary with a good battery. You ever seen those hand crank flashlights? It's very much the same as those. I'm actually one of those 0.01%'ers that would benefit from a regen hub. I pull a single-wheel suspension trailer for extended rides that I could install a hub motor only for its capture ability. On descents using the motor for regen would slow the bike and in the process decrease brake pad wear... that's almost more important than the minuscule amount of recaptured voltage. The point is that it's not even worthwhile for me and how I ride at this point to pull around the extra weight of the motor... let alone the additional cost.
The question you have to ask yourself is why would anyone choose a hub drive in the 1st place... even if it is sold on its capture ability? Why? Because they are cheaper and a little easier to mount on a bike. Are you sensing a theme here?
Someday they will have regen for ebikes that actually work until then people will try to sell these.