I have a 20 and love it. It is stock except for some trigger work. I also find it to be just about perfect for the woods and deserts I like to play in. I took it up to AK with me on a moose hunt and I wore it for 12 days straight.
I have killed some pigs with it in TX and I like it for that as well. We hunt with dogs, so shots are close and it does not over penetrate like a 44m. or my .45 Colt loads do. This is much safer for the dogs and a catchers. It is great to carry 15 rounds in such a light package. It allows me to go off hunt all day and not have to worry about carrying extra ammo in the saddle bag. An extra mag makes it 30!
I like those chest rigs you linked too. A bunch of the AK bush pilots carried 20's in chest rigs like those. I also like the ones made by Grizzly Tough:
http://www.grizzlytuff.com/I could even get 10mm out in the little village of Aniak.
Great gun, I highly recommend them!
Matt