I wouldn't write the regen off my wants list because it doesn't do a very good job of charging the battery. It's a very good option/ability when riding in areas with long hills (coastal, foot hills, maybe slightly mountainous). Flat landers will have very little use for it.
It might be easier to understand if they called it something else, like a motor brake. Though it works by turning the motor into a generator with a huge load on it (the battery), it's primary function is more like an engine or diesel exhaust brake, which produce a lot of drag on a vehicle, but will not actually stop it.