I think in the end Mike Petro may be correct in believing it may ultimately come down to temps used. I don't understand all of it, but enough that it seems a valid theory.
Just a Clarification:
The work that Mike has done is in regards to the Formation of Formaldehyde and Acetaldehydes in e-Cigarette vapor.
And in those regards, Yes... Coil Temperature is the Major Factor.
New studies find carcinogens in vg and pg at high temps, even in tootle puffers
Nobody even mentions if he managed to quit smoking altogether.