I'm on Week 2 of my usb passthrough from PureSmoker and haven't had one ounce of drop off production yet. If you are constantly vaping on it.. beware.. the atomizer can overheat and boom no more vapor. It will fry it if you are not careful. I usually check mine after about a cigs worth of hits (10-15 draws)to make sure the atomizer is not getting too hot. As long as you keep an eye out on the atomizer you shouldn't have any problems making it last imo.
When home, I alternate between the passthrough and my stand alone pen. I am a heavy vaper and yes, it can heat up. That seems to solve the problem for me.
Lu