I can't speak for the WSM but I can tell you the Smoke N Pit is not a good way to go, especially starting out. I've owned one for several years and it's near impossible to get consistent results with it. It has way too many air gaps to be able to keep a controlled temperature. I recently built a UDS and my BBQ has seen a significant improvement overnight. Don't mess with the SNP!
Brinkmann Smoke n Pit
Weber 22.5" OTG