At least on my set-ups I would have to put so much rubber Cathwiskers onthe string to equual the leeches effectiveness I would loose 8 FPS or so. Instead I only lose 2-3 w/ the Leeches.
Durability is not great and If you have a bow w/ alot of string vibe in the first place (Mathews Q series bows are notorious for this) then theyw on't last more than a couple of hundred shots.
They work so well w/ so little speed loss that I don't mind buying new ones every couple of months.
JEffB