And when I was in school half the kids smoked cigarrettes. I have no idea what the numbers are, but you have to consider that fewer kids are using tobacco, which is a good thing.
As far as I remember, the vehicle is propylene glycol. It isn't biologically inert, and I'm not sure how much work has been done to study buildup within the lungs or combustion products. Combine that with dodgy sourcing allowing metal contamination.
It seems more or less the definition of trading the devil you know for one you don't.