In the study, participants were given 13 weeks worth of supplies, then were interviewed six months later to get the results.
Two things I noted. One, what do they mean by 'commercially-available' e-cigs? As we all know, not all e-cigs are created equal. Were they give some disposable kind with only one flavor? Heck, I wouldn't have quit with them either.
The other thing (not mentioned in the article) is that nicotine-containing juice is illegal to buy in New Zealand. So the study subjects - after they finished their 13-week supply - wouldn't have been able to get more unless they ordered it from overseas. Not that that's impossible but it would make it harder if someone wanted to just continue vaping ejuice with nicotine in it.