Traditionally, a charcoal kamado is a Japanese earthenware cooking vessel. The most common version today is a hinged ceramic pot with grates, airflow control ports. because of this construction, they are often referred to as ceramic grills. While very simple in their design, the quality of the food they produce has generated a cult following for these grills. Ceramic grills are also much more weather resistant than metal grills that have a habit of rusting away in many climates.
Much more temperature control and stability, less airflow results in more retained moisture in foods. Charcoal always burns at the maximum volume for the allowed airflow, therefore, controlling airflow is how you regulate temperature. Because a low and slow cook can run 20 hours the volume of air flow and evaporation it creates dramatically influences the moisture content of the final product. The thicker walls of a ceramic grill create the thermal mass giving it stability and reducing heat loss. Metal grills on the other hand absolutely radiate heat and require more fuel and airflow to maintain the cooking temperature. With a metal grill as the ambient temperature changes, you must adjust the airflow to correct for the changes.