That item has nothing to do with woodworking but a lot to do with safety. It came along years ago when bicycles were the main mode of transportation. Many attempts were made to produce a seat belt for bicycles but all went nowhere. This solution was perfect. You simply turned the key apparatus to line up with the seat lengthwise and in one quick movement, facing side on, with your back to the seat, you hopped up over the seat and came down swiftly, at the same time you swung your leg over the cross bar and twisted your body to face forward as you landed. A perfect manoeuvre would place the key in it's optimal position. Mind you it did take practice but one would never have the fear of falling off. Some became very adept at this procedure. Others would try again almost immediately after they were discharged from the hospital.