I guess you really don't have tyre balance problems at very low speeds. But I have been mucking around with them all day (as you would) and I can't fault them so far at any speed or any surface. Amazing really.
Mine were $20 a bag (for 8 oz size) - but when you consider that you never need to balance the wheels again - I guess it's a bargain. And maybe with some Patrols it may even fix the 80 kph vibrations? It would be interesting to find out.