The pocket operators feel quite fragile without any protection around them. Even if they are quite sturdy on their own, having a protective casing around it allows you to carry it around in your bag without worrying as much.
The casing can be a little difficult to fit onto the PO, but it's made out of a flexible material so you'll get it on there eventually.
The pictures on the buttons don't explain their functions as well as the text under the buttons on the PO does, so it took some time for me to get used to the new look.