just get a pump kit with two guide rods and it eliminates the need for those. I have a friend who has one on his black magic pump and somehow he bent the cocking rod and now it binds and grinds in every stroke.
for the money, it helps minimize the slop in single rod pump kits. also helps to get rid of barrel rub. i did some testing and a write up for gat a little before they came out. see if i can find the link... as for the poster above i dont see how this can bend a cocking rod since its basically independent of that mechanism. the only thing it touches is the pump guide (which its mounted on) and the pump arm (which the arm slides thru the "guide"). these are the only two things that this acts force upon.