IMHO it is inconsistancy of the manufacturing process. I have used over 100 atomizers, and find vast differences in draw, flavor, life, et. My best one just died, it was my first from Jane, a pen style. I have 6 Janty classics which are da bomb, 4 from Jane, and 1 of my original from Njoy. I have yet to get the SD working right, tried 8 atomizers. I dunno, I am thinking of trying to have em made, here in the states. Seems china is so damn inconsistent. Hopefully the newer models will bring us what we wantproper draw, consistant burn/flavor, and batteries that keep the same level of heat. Go figure, maybe we can get, what we need, for the new year.