There were 28 gauge guns that were really neat just because of their compact size. It was almost like shooting 3/4 scale working models.
Those guns were neat, but there is nothing special about 28 gauge. It's basically a light 20 gauge in smaller package. No magic. 3/4 ounce 20 equals 3/4 ounce 28 gauge. Same thing. But some people like it because they can shoot it like a 20 and pretend they are using what used to be call "a little gun".
28s have great snob appeal too....sort of a 20 gauge for snobs. You can strut around in tweeds, and speak with an English accent, and say things like "By Jove, that's such a smashing little bugger."
And the ammo is really expensive. Sure you can reload. But if you are going to reload, then you can reload 3/4 ounce 20 and have the same thing.
But some of the 28 gauge guns are really cute. If you are looking for a cute little gun, then by all means get a cute little 28 gauge. But a 12 gauge o/u with 28 gauge tubes isn't cute.