You have 2 possible heights, see 3 by removing the grid below. This allows to adapt the wrist rest at best depending on your position at the keyboard. By removing the grid, the underside of the wrist rest is smooth and adherent to avoid slipping on a desk.
The above is not plastic but a kind of nice fabric, so that it is not cold to the touch and does not catch dust.
The plastic grid is not breaking hard but flexible plastic.