If you get a good one, they are awesome! I have a dual fan setup that blows quite a bit of air and made a huge difference. I was really struggling when it was in the 90s to keep mine cold....put this baby in and I can now keep popsicles in the freezer. The upper fridge was in the mid 30s and the lower in the mod 40s.
I will paste the link below to where I got mine, but be warned - it does take some install work on the newer Norcolds. Not bad, but I had to snake a very thin wire down the drain tube, around the fridge wiring and down to the fuse load center. Anyone who likes to tinker should have no trouble installing it.
Not sure it would save much on wear and tear, but as a side benefit it gets rids of most of the frost on the rear cooling fins.