Fair enough, I've known people to go both ways on that. I just buy the OE Firestone ones through eBay, they come with the new OE solenoids and O rings. That being said, if I could just get the Firestone air springs by themselves for say, $240/pr, I'd do it. The solenoids rarely go bad. I've only seen it happen once.
Say you're just going after the air springs then. (I didn't realize they came with new solenoids.)
Arnott units are $198+shipping, so say $220, assuming FEDEX or UPS.
It just depends on how long he wants to keep the car, and what his preference is for replacement parts.
I will say this.
When I bought my current car, it had Arnott air springs in there already. The car was sagging a bit, so I opted to replace them. In the time that I drove it with the Arnotts, I did not notice a difference in ride comfort from the new OE ones I installed. In fact, I figured they were the original Motorcraft ones in there.
So, if you're concerned about ride comfort, as best I could tell, the standard Arnott air springs and the OE ones ride the same, or, so closely, one could not easily percieve the difference.