Ya, I like them and have used them in MP games. Usually on the border and at chokepoints to keep enemy dominion out.
In Dominions 2, I used to give them the fire helmets which gave them a flame strike attack, but that's no longer available.
But they're still good for the other things mentioned by others. I hadn't really considered the MR 18 soak potential but for certain hostile magics, I can see that's another possibility.