Doing a review of the current research isn't valuable for the reasons I outlined: overall research is immutare so an overall review isn't going to be that insightful right now.

Here's an example of a gaping gap in research on e-cigs: "To our knowledge, there are no relevant study in humans on carcinogenic effects from pure nicotine including products, such as NRT and e-cigarettes." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4553893/

It's really hard to summarize a body of research if there's barely any research been done in an area.