I really want an 18" WSM, but can't afford a new one at the moment and don't want to bother with an ECB. Now and then a WSM will show up on on Craigslist for cheap, but someone always beats me to it.
In the meantime, I have had some success using my Weber One-Touch grill as a smoker. I've perfected my ribs technique and did a pork butt that turned out pretty good. I've been able to get at least 8-hours sustained at 225-250 degrees without adding any charcoal.
So, other than limited space for food, what are my downsides to just using the kettle? What will I gain with a WSM?