Reviews that do not agree with Cheng: 
 :::* Electronic cigarettes (e-cigarettes) provide nicotine via a vapour that is drawn into the mouth, upper airways and possibly lungs [2,3]. [(Brown et al 2014)] 
 :::* Drawing air through the e-cigarette triggers the heater to create vapour which contains nicotine and is inhaled (Public Health England 2014) 
 :::* powered by a lithium-ion rechargeable battery that is designed to vaporize nicotine to be inhaled (Caponnetto et al 2012) 
 :::* work by vaporizing a solution containing nicotine dissolved with flavorants in a carrier medium (usually propylene glycol (O'Connor 2012) 
 :::* They are battery-operated devices, used to vaporise a liquid that may or may not contain nicotine. )(Farsalinos et al. 2014) 
 :::I can find loads more. So relying entirely on Cheng is not acceptable.