I have the Dutchman Boom brake
. It's pretty much the same but I would not go out with out it now. I just about tore my arm off on an accidental jibe once and that was enough to convince me that the cost was nothing compaired to the pain a boom can conflict on a person.
You won't need to set up a preventer ever again. But you do have to get the attachment points in the precise spots for it to work 100% the way it's suppose to.
And Yes, go with the line size it recommends. Too small will cut into the sheaves!......................._/)