Definitely a "must have". Mine has just one really nasty gouge on it. Don't know when it happend but I'm sure glad ithe guard was there! Other wise I might have been pushing my bike out of the woods.
I haven't compared many other bikes but it seems that on the KDX the water pump is sort of vulnerable. On my freinds KTM 300 the water pump is mostly "protected" by his stock pipe.
The Devol water pump guard is a relatively low dollar item...definitely worth the small investment.
Just do it,
Chuck