The lead basically is around your NECK! If the dog pulls to the oposite side that it is looped over, your neck will get the full force pulling accross and down on it. Just imagine your dog sees a squirrel, rabbit, cat etc.....
It would be pulling before you could react with your hands and the force on your neck would NOT be progressive but a SHOCK, and could result in quite serious injury, akin to whiplash, OR WORSE:yikes:
If you're after hands free walking or a device to give extra security in case you let go of the lead... get a walking belt.
Only my opinion, but I would hate to think of anyone getting hurt.