I would suggest that the following needs to be taken into consideration:
While it is clear that e-cigarettes are far less harmful than
tobacco, nicotine does have some negative health effects, but the long term health impacts of using e-cigarettes are currently unknown;
Expanding on the previous point, it may be appropriate to require e-cigarettes to come with a general health warning such as "may damage your health" until evidence is available to make a more precise warning;
There are currently no standards in relation to the quality and safety of e-cigarettes, something which needs to be rectified for reasons of consumer protection;
The aim of regulation should be to keep e-cigarettes available as a
harm reduction tool for adult smokers, while taking every precaution to ensure their use does not "renormalise" smoking and that they are not marketed in a way that broadens their appeal to non-smokers, especially young people. In order to guarantee this, it may be necessary to subject e-cigarettes to marketing restrictions such as minimum age of purchase requirements, forbidding free samples or below cost pricing, a ban on characterising flavours (e.g. chocolate) and advertising restrictions such as prohibiting billboards near schools, daytime TV adverts and adverts in magazines, websites aimed at or read by young people.
Following on from the previous point, e-cigarettes used in public places where smoking is forbidden or in front of children would also contribute to "renormalisation", so steps should be taken to avoid this, for example restricting the use of e-cigarettes in public places.
This is indeed a complex issue, with many different viewpoints.
I am open to comments and suggestions.
