My husband started smoking a eGo-C Twist with a 2.5 ml chamber and 36mg fluid on 7/13 (he goes to a local store for his fluid)
He hasn't had a cigarette since the end of July (when he switch stores because the one was cutting their fluid with something and it burned his throat)
It literally costs less than half as much
The only thing in the fluid is nicotine, flavoring, and vegetable glycerin (which makes the smoke).

Pros: His smoker's cough is gone & his blood pressure is down! He no longer smells like cigarettes every time he kisses me (he smells like peaches or lemonade now, and that's only if he has JUST taken a puff). He's tried quitting a dozen times before and never been able to actually go cigarette free (he tried the patch, the gum, cold turkey, and just about every other way) and this time he has.

Cons: You have to be careful who you buy fluid from, there isn't any regulation on it yet. Disposable ones aren't good for a serious cigarette smoker (those who smoke more than 5 a day) wanting to switch. Some people use Propylene Glycol (animal based fluid) but DH has had better luck with vegetable glycerin.

I can't say if they are good or not, but they did help my FDH to quit real ciggies. About 4 months on the e-cig (sorry,don't recall the brand), and he started tapering off and hasn't touched any nicotine in well over 18 months (wow, I think it's probably pushing two years!). I figure any health issue associated with 4 months of e-cigs is probably far less damaging than an ongoing pack-a-day habit.