I have the 22.5 WSM and the Onyx. I like both, but I would take the Onyx hands down over the WSM. Here are my reasons:
1. 7lbs. of charcoal will last you 15+ hours at 250 degrees. ( I have gotten 19 hours).
2. You can shut off the smoke and turn the Onyx into a oven.
3. Three sheves are accessible without moving racks.
4. The Onyx has a door versus a lid.
5. Wind is not going to impact the Onyx like it will the WSM.
Those are my thoughts (unpopular as most will find them).
Peace and Smoke,
My Weapons: Custom rig - Kandi, UDS; Bubba Keg; 22.5 WSM x 2; 18.5 WSM; BWS extended party; BWS Gator and an Onyx Oven; 29' ft Coachmen Leprechaun (Lola).
Dan Chambers get well soon, so we can tell you to "Shut up Chambers"