I have the big one and it is just about right for my Jumbo Joe. The big chimney holds just about enough to fill up two Weber CharBaskets. I wouldn't want a smaller one for a 22" kettle or even an 18" kettle. You can alway add less coal to it if you find it holds too much. I even use the full-size with my Smokey Joe and fill it between 1/2 and 2/3, that works great for me on the 14" grill.
I had a smaller generic chimney for my Smokey Joe, and it worked pretty well at first, but the metal started rusting and flaking and eventually the stupid thing rusted in half at the joint where they welded it together. When I say it was generic, I mean it was a no-name, made-in-China, $5 special at Walmart.
I think I got about a year and a half of use out of the no-name before I decided to get a Weber chimney. This is my fourth year with the Weber chimney and it looks used, but not rusted or corroded or anything nasty like that cheap one.