But I still don't understand why YOU need them. What problem do you have?
Any decent fitter will use a dynamic balance machine which gives 3D balance to within a gnat's nidger. Unless you have a dodgy fitter, shot bearings or something loose in a tyre, then why have something else floating around.
Slime and other stuff floating around in a tyre I can understand as it is a preventative rather than a cure. But in this day and age I can't see what you are trying to cure.