Depending on driving conditions and terrain, regen typically increases an EV's total range by 10-40%, that's probably what he means. And yes it should be 90% efficient in recovering energy (when it can, regen doesn't work under a certain speed or if the driver brakes hard enough to use the brake discs). Neither one has any effect on one-pedal driving if implemented properly. The Leaf does one-pedal just fine until 4mph when the creep comes on (for no reason arrgggggg I hate it).
I got my Leaf Box and made a video: