I have used the M401 to stop smoking. It's been about 6 months now and only had one puff at ASE when my batteries died.
I think the 401 is closest to a real cigarette and decent vapor.
The screwdriver looks like a beast as well as other of the hand held higher voltage ones.
From the reading I had done the nicotine comes in different levels typically 0-36 mg of nicotine per ml I believe. When smoking a cigarette I believe that it is about 7-12 mg; however the delivery of nicotine in cigarettes is aided by the other chemicals. This is why, even at 36mg, there is a chance that you will not get the same amount absorbed by the body as the "smoke" in e cigs is based on vegetable or normal glycerin. This is a poor delivery method as it is an oil base.
It is possible to overdue it and get nicotine poisoning but to die from it someone would have to be pretty stupid as you get an awful feeling from nicotine poisoning and you really cant smoke anymore.
Tobacco flavors are pretty sick too, as they are trying to replicate the flavor of smoke which can't really be done without smoke. I currently have clove, menthol ( which is just mint no tobacco), strawberry, cherry, cola, vanilla, cappuccino , grape, apple, red tea, cream and pear. They are awesome, except cream which tastes like coffee cream....
If anyone wants a hook up I do have a guy in China that sells it at wholesale with a 1 year warranty I believe. Just shoot me a pm and ill send out his email address and im contact.