KKM's website is apparently down...
Lone Wolf has ported aftermarket barrels for G20:
http://www.lonewolfdist.com/Products.aspx?CAT=236
I think you'll find Lone Wolf's pricing the sharpest, and they're an excellent company to deal with!
You can put a
non-ported barrel in a compensated Glock, but you should not put a ported barrel in a
non-compensated Glock.
Some owners of compensated Glocks drop in an aftermarket,
non-ported barrel, for self-defense use, as they don't want those upward gas jets in that application. When this is done, the gun shoots and behaves like a non-compensated model.
Drop in barrels are just that--good to go, as is.
Semi-drop in, or fitted barrels, require some filing and fitting before they're ready for use.
--Ray