There are lots of different styles of this product available, they all do the same thing, or are supposed to. The wire mesh attracts limescale more readily than the surface inside of your kettle.

You pop one ( or two ) inside and leave  it there, the limescale builds up on the mesh instead of the kettle, when the mesh gets clogged up you rinse off the limescale and reuse it.

Although many of our vistors use these and claim good results ( which is why they are included ),this is not our preferred choice as we don’t like the idea of a mesh ball rolling around on the inside and possibly scratching the surface ( especially plastic kettles ), also if you forget it inside for too long bits of limescale can break off and float about inside the kettle.