It is easy for us to spend your money. I am not familiar with the Pathfinder diffs, but I am a believer in armor on the underside. It is kind of like a fire extinguisher, you feel good if you never need it. You only need it one time.
In my opinion, if the diff can be dented to the point of hitting the ring gear, the diff needs armor. I am not very concerned with damage to the cast portion of the diff, it is very tough. The skid in the link appears to be more for skidding over things, than protecting against damage. Personally, I would not put it very high on my priority list. If the opposite side of your diff is like the sheet metal Samurai, that is what I would want to protect.
The axle part of the diffs on my Samurai are sheet metal, with the plug on the bottom. The third member (ring and pinion carrier) is cast steel. When I built my Samurai, I did put armor to protect the sheet metal from bending in against the ring gear. I thought it was a waste of time, and only offered bling-bling. That was about five years ago. I ran a trail last month and I honestly can say I doubt I would have driven home had I not had the armor caps on my diffs, front diff and rear diff. Underneath my Samurai is painted black and white. The armor diff caps are white, and show wounds received protecting the ring gear. I have scarring of the paint on the cast part of the diffs and drain plug, but absolutely no damage. I might be able to post photos, if anyone wants to see them.
You only need one fire to need an extinguisher, and only one rock to waste a diff. Personally, I have never needed an extinguisher. I suggest you look at a 4x4 site and see what they do to protect the diff on the Pathfinder.
