I think the metal sleeve is only available for the full sized nauti, but could be wrong. Haven't paid much attention to them since I went RBA. The smaller AFC holes will give yo more flavor and conserve juice, but the bigger ones will give you better clouds. Make sure you keep your tank clean. You will find a small amount of juice in the AFC chamber under the coil once in a while no matter what. Vapor will condense in the draw tube and settle down there. Every few tanks or so, pull the coil out and give the base a proper washing or this condensation will turn to a nasty sludge. As the coils age, you will likely find yourself messing with the settings again since the coils start to wear a lil long before they are goners. You can prolong their life by gently, and I stress GENTLY cleaning the metal screen on the top of the coil. It will gunk up and hurt flavor production. I used a clean, dry paper towel to blot the screen. If you ever accidentally damage the screen or it sticks t the towel and comes out, the coil is a goner for sure. Some folks say you can soak the coils to clean them, but I never had any luck with it. But you have a solid piece of gear to vape on.