I believe the ball HAS to be shiney otherwise you would get the 'creak' they are famous for.
I don't think they serve a very good function particually when ATC is fitted and I would like to go back to a greased towball when we didn't have problems!
Cliff
The AKS and ATC address quite different issues, though complementing each other.
The AKS only damps, and marginally to, the inevitable minor sways a trailer exhibits from a multitude of disturbances, which then get reflected onto the towing vehicle.
Its purpose is to make towing less stressful and uncomfortably so less fatiguing for all onboard. The pitifully small amount of friction on a pivot less than an inch radius, can in no way tame a natural frequency snake.
Pity generic friction dampers of all flavours ever got called "stabilisers", as far too many people assume that implies a great deal more ability than they can ever offer.
That true stabilising role however is where the ATC comes in, on territory ways beyond the AKS's role. It can tame a snake, having the vehicle's pulling "power" and caravans brakes as a lot more effective tools to do so.
Greasing the ball, loses that more damped towing experience.