My only experience with the green slime used for tire repair...sort of like fix a flat. It didn't unbalance the wheels but they had old fashioned lead weights anyway. I would think that it would NOT be a good idea because you would ultimately have more spinning weight in the tires slowing handling, and adding unsprung weight is never a good idea. In fact, if you have ever ridden a bike with magnesium, or other very light wheels, you will attest to the remarkable difference in handling reducing unsprung weight can have. This is why every year you see lighter and lighter wheels on the latest sport bikes. I think MO had an article with an RC51 that has carbon fiber wheels or something and mentioned how much the lighter wheels helped the handling. It seems like it would be important to just add enough weight to balance the wheel and nothing more.