Re: In the market for a new cooker
The better sealed the cooker is the less airflow you need and the more efficiently the charcoal burns. This means that your food will be more moist and you'll use less charcoal. In general the biggest jump is from a steel grill/smoker to the modern "ceramics" (most of which aren't really ceramic, even the KK is a more advanced refractory material that's better than fragile ceramics), but there is some difference among the ceramic varieties.
How many ways can you set it up? I'll answer with the question how many things do you want to cook? There's both direct and indirect methods, with smoke and without, there's a rotisserie or on the grill - and the grills can be at multiple heights. I think you'll be hard pressed to find anything you can't cook, bake, or grill on the KK.