Good question. My own take on this, and without ever having used an external smoke source is that smoke flavor is smoke flavor regardless of whether it be hot smoke or relatively cool smoke. Hopefully someone with experience using an external smoke device can provide some solid insight as to the flavor profile. Regarding layers, I would think (after ruining a butt) that the longer a piece of meat sits in a stream of smoke, the more flavor it gets, at least on the exterior. My ruined butt was very bitter, and the tacky coating on the exterior had the consistency of creosote.