I have read a few places that the m401 is the "slightly cheaper" version of the 306, how true is this? and if so, how can i tell which one i have? i bought a branded e-cig and i was pretty sure it was a 306 until i happened across a video of someone with an m401, i noticed that it looked exactly the same in all the components, but didnt produce a lot of vapor. Any tips on telling the difference? the supplier i purchased from doesnt offer replacement parts for my unit, so it would be great to know what to look for when the time comes to get some spares.