I have a Kamado Joe classic(regular). Wife got it for me about 4 years ago & I love it. I use it 3 to 4 times a week.Before that I used Weber kettles. Had an 18 & 22. Upgraded to a Performer in 2010, loved it. After the KJ the Performer has been used about 3 times. I have used it for low & slows, grilling, pizzas, etc. There isn't anything I have done on my KJ that I can't do in a kettle but for me after learning how to use the KJ it is easier to do all those things. It can be ready to cook in about 15 minutes for the evening dinner cooks & it great for over night cooks. It is much more efficient than my performer. As far as capacity I cook for just the wife & I so I don't want for space(an 18" weber grill fits right in). The most I have done at one time is 2 whole chickens & 2 racks of baby back ribs on it at the same time(2 sitters & rib rack). They have an grate expander which enable 3 levels of cooking, if you so desire. I can't compare it to a WSM because I have never used one.
There are drawbacks, it takes a lot of time for it to cool off enough to cover after a cook. The KJ doesn't have a rain cap like some other ceramic grills so water can get in the daisy wheel in the rain if not covered. It is heavy but very easy to move if necessary via the cart in came in. I don't move it that much but I didn't move the performer that much either, usually moved arond to clean the patio. I have found that after getting over the learning curve I feel the "human element" to fire management gets a little lost. It is a little surreal to throw a rack of ribs on & not have to touch them for a few hours, unlike the the Weber where I was tending the fire much more closely. That being said Weber was about 4 years to late, had a product like the Summit been around back then I would have snapped one up. I think its a great deal that you are getting & I don't think you would be disappointed if you put in the time with it.