My bow came with string leeches already installed so I don' t know what--if any--difference they make. I thought mine were going to last forever until I read a thread here recently about them breaking off at the " turn" towards the tip. I thought mine were fine until I looked and saw that one end was broken off of each leech and the remaining two were getting there. I was told by a pro shop owner that they last longer if you wrap a piece of moleskin around the center before installing them--kinda like the peep-tubing idea, but I doubt that either of those methods would prevent the ends from breaking off.