Just got my K100 today from Fast Tech. I Love it......however......if you get one, clean the 501 connection before using it. I put on a Boge F16 carto tank that I was using for two days and when I put it on the brand new k100, It suddenly had a machine oil taste. After a half our of vaping it on and off hoping the oil taste would leave, I cleaned the connection (saw an oily stain on the cloth), changed the carto, and the oil taste was gone. I don't think there is any pre-cleaning done before they ship them out.