They worked most of the time. But hitting a rough section on the highway would knock thinks out of balance, and it could take a minute or two for it to get back into balance. Now, I just make sure my tires are done a dynamic balancer, like RoadForce.
18 wheelers use a similar thing. They work fine for that application, but I remember reading that there is a limit to the speed the wheel can rotate at for them to work, as passed that limit they just follow the wheel round. I think it was something like 70mph, although I'm sure it will depend on the wheel diameter.