I took a stock bike all over the USA:
Moab:
Yes, you can see a chunk is missing - I hadn't even noticed until I saw this photo - goodness knows when that happened?!
The Rubicon:
So as GLUGo says, the stock plastic one is actually pretty tough!
However, I did fit the OTR one for Heroes-Legend:
(ok, not that you can see it in this picture)
And I'd say it is a very good option if you'd feel happier with a piece of metal under your engine... it's neat, strong, and fits well.
Personally I don't feel you need a huge tube to protect your waterpump, but others will differ and maybe I've just been lucky... but certainly of all the 'heavy duty' options out there, I'd go for the GiT one from Adventure Spec as the most solid and well-considered design...
That's not actually much help is it? but hey, it's an excuse for some nice photos x
Jx