I won't even touch the health effects, because that still isn't clear.
But teen use has been skyrocketing:
Teens who vape are ~4x more likely to start smoking than teens who do not vape.
The studies about how effective vaping is as a means of smoking cessation are pretty mixed. It is entirely plausible that vaping could end up acting as an on ramp to get more people to smoke. Its still pretty early to tell, but the current trends are concerning.