Hi JDL,

In terms of fit and finish, to me, the listing is: 21/22 series, ZG47, early ZKKs, CZ550, late ZKK.
In terms of general design: ZG47, early ZKK, CZ 550, late ZKK. I have mixed feelings about the 21/22. If not for its double triggers (very few came with a single trigger from the factory), I would rate just behind the ZG47.
I have, and have had, early and late ZKK, and have closely seen the superb ZG47 and 21/22. And fail to have both by my own stupidity....I still kick myself...

PH