My 2017 came with those installed, not sure if they still do that though.
Anyway, the first week we had the rig home I drove out of a parking lot and dropped the real wheels into a huge pothole. Said pothole being full of water and not noticeable. The skid wheels hit and protected the sewage connections / bumper / etc. I know they hit hard because there are pock mocks in the skid wheels where gravel got embedded in them. I think they are aluminum but not sure.
So to me they paid for themselves that day, anything else is just extra.