My first USB m401 passthrough was from a US vendor and cost $30 and lasted about a month. Now I get them direct from China for about $7, but they only seem to work a week or two at most. My first atz was from a US vendor in an e-cig kit and lasted 6weeks using it with batteries and the next ones that I bought cost a bunch , so I starting buying them from China. The first order seemed fine, but then they didn't last anywhere as long as my first one, but some of the last order are lasting as little as an hour! BUT, I'm using them with a USB and a Kennsington power supply. So... is the usb just more powerful and burning them out or are they just crap? Batteries only lasted me about 1 hour, so I obviously am vaping a LOT, which is why I went to USB! I also noticed that my first 30ml bottle of juice lasted well over a month, but now are lasting about 2 weeks tops, but it could be because the azt's are just not performing well. I feel that I have to drip 4-5 drops in the cartridge constantly to get a good vapor and sometimes that azt gets so hot that it almost burns my lips. Any others out there seeing this with their usb and atz? or am I just having hallucinations from vaping so much?