I disagree with him. I think verbal commands are significantly better than visual. With visual, the spotted needs to be in sight at all times. If you are trying to watch a real axle, you wont be in sight as you are behind the vehicle.
Verbal commands also have a wider range in communication.. "front tire bumping up" "rear passenger tire dropping" ect.
He hand signals to go left. Is that a HARD left, or a SLIGHT left?
I vote voice signals. Not hand signals.
Besides all that... How am I supposed to hold a mountain dew if I am using hand signals??