When I was a youngen riding a TY80 doing shows and parades with my Dad and Brother we had the same type of set up. This would kill the engine if we fell off, lessening the chance of a spectator being hit. Dad also added an Emergency brake to his Reflex, not exactly sure how it work but there was an electric motor that would pull the rear drum brake arm engaging the rear brake. I think he had a second set of points on the handlebars that would engage if he was separated from the bike.
When riding I never even notice having that bit of string on my wrist. (Left side)
(Side note: We called ourselves Team Thud...........that sound that is made when the human body contacts the ground after falling off the bike)