So, I agree with the assessment of the Nautilus clone heads. Just as good as the real ones. My experience with the Kanger dual coil w/sleeve clones (from fasttech) is that a) they perform as well as the real ones, but b) they are constructed of lower quality material. If you rebuild them, the chimneys need to be removed carefully. They will snap off if you try to wiggle them and even moderate pressure from pliers to pull them off can crush them flat. YMMV.