I have two kongs. One is on my lineman's belt that I do use when one sticking. The other is on my tether I use at hanging out. Personally I feel more comfortable with rope to rope hitch when one sticking. Should I fall, I have seen videos where mech. Devices really damage the rope.
Also one of my ducks gummed up last season, and was not clamping onto the rope. I was a few feet up messing around with something, and the rope kept sliding out. Took 10-12" to catch and stop. Prussic knot is pretty fail safe. IMO.