the stick guards on mine are the plastic ones and i haven't had any problems yet. i think that Kubota offers a steel set although i haven't seen them. there is a member here that makes an excellent set for the older 1100 series but they won't work on the X series.
I got the metal ones but they are same size and position as the plastic ones. When I saw them at the dealership I bitched because I expected them to be like the full size ones that cover the bottom and sides. He just took them off the bill and said keep them not worth the labor to replace them.