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I've seen them used, they work if your bobbers small enough, that bite was so light 
you had to watch your line instead of the rod.

Used to fish the east side of the US Steel break wall in Gary in the eighties.  Parked at Lake Street Beach and had a little bike rigged up to get there(2 mile hike).  Used baby pond crabs with a slip bobber and would catch some darn good size perch with this rig. I would hook the little crabs in the tail.  Was going to try this In New Buffalo but found out using crayfish are illegal in Michigan.                                                                    KJK