Open ended slings? Never heard of such a thing, and would be very hesitant to rely on a knot or hitch when lift or hoisting 5000 plus pounds over a house or two. I use 25-30 foot eye and eye slings. Presling as many as possible without running around to much. If its not preslung, I am waiting at the sling area, unhook from the ball, sling around limb, rehook to the ball, descend down and get into cutting position.
The beauty of really long slings is you can sling them higher up and you can usually attach them to the ball from your cutting position if they are preslung. I generally work with a second climber on big crane jobs. One climber sets slings and the other sits lower cutting. It works well. And before the critics pipe up, Im talking HUGE trees with huge cranes not jib trucks designed for setting pallets on rooves. Usually 165 ton, with extra counterweights, 180 feet of reach and taking picks that average 5000 pounds or more.