Check out
This Briefing Document that was linked to in a post elsewhere. In section 1.3 , it cites a U.K. survey suggesting there are 2.1 million eCig users, with 700,000 being ex smokers and 1,300,000 dual users. That implies about a 1/3 quit rate of all eCig users, and surely many of those 2/3 dual users have never intended to quit or tried very hard.
I agree; I get PO'd when I read things suggesting the quit rate using eCigs is very low. Stalinist lies at it's worst. Anyone that vapes or knows a bunch of people that vape know the quit rate is very high.