Carl,
I assume that you were referring to either a balancing material added inside the tires, or possibly the CentraMatic wheel balancers.
I don't know about the balancing materials added to the interior of the tire, but I do have experience with the CentraMatics, as I used to run them on my Peterbilts when I was still involved in the trucking industry. I had them on the steers and on the drives and they were great as long as you started with a good set of tires to begin with. I typically got 90 to 100 K on a set of steer tires before I pulled them off due to increased wear on the outside edges. After that I'd run the tires out on the drives during the summer months, just to get my money's worth out of them. I always pulled company trailers, so did not have the opportunity to try any out back there, but if they work as well there or on your fiver as they did on my OTR trucks, they are definitely worth the money.