I'm a professional stringer. I've used this product, or something like it, for decades. It keeps the strings from moving around, which is death to 17 or 18 gauge string, and an absolute must for gut, any gauge. Also, it adds a little tension back to the strings, which sometimes losses a little tension at tie off in the stringing process. Oh, and please, string-a-lings do not effect the trajectory, or the spin of the ball. If usage of string-a-lings were good enough for Sampras, and a number of other world class players, it should be good enough for armatures.