In standard aerators with a strainer grid a water film arises. The water film forms a bridge between the aerator and the housing. At that point lime starts to form which clogs the air slots. So the stream gets hard and splashes.
However the R.C. Mannesmann aerators make the bridge formation more difficult. The unique structure reduces the lime formation substantially. Even after a long period of use the stream stays straight, round and splash-free. Moreover, the removal of limescale is done with simple hand movements.