Well is it 20 or 22s? Are you sure they are same width and offset as your 18s? If not could cause you to have rubbing issues.
Agree with less side wall flex so cornering will be more stable. Less tire so yes it will be rougher. As far as looks to each there own. Don't see them being any louder unless I missed that its a different tire? Toyo m/t 35x12.50R20 and 35x12.50R22 shouldn't be any louder or quieter then the other.I'm thinking they might be a lot louder and ride rougher than the 18's. But if you like the look better and don't mind the noise, go for it. It should handle better in the corners. But it's not a sport car either. I wouldn't do it.
And why does he want to trade? My guess would be noise/ride quality issues. And I could be way wrong.
There you go. Just have him put it in writing about the switch back.He just likes 18's better is all, we can switch back anytime, or never.