I'm thinking of articles like https://www.scientificamerican.com/article/is-nicotine-all-b...
I'm obviously talking about moderate doses. I know concentrated nicotine is very toxic :)
Best summary I'm aware of (note the many caveats): https://www.gwern.net/Nicotine
I am a pretty serious athlete. Vaping - whether it was 3mg or 0mg e-juice - fucked with my lungs pretty badly, and caused a noticeable drop in athletic performance. Also made me feel way less motivated to lift weights and train, which I chalked up to the instant gratification of nicotine. When I did lift weights and train, I always felt like I wasn't able to give 100%.
I quit, but goddamn it was a pain in the ass to quit. It's not even the nicotine I miss, really, so much as it is the whole experience. The heat, the vapor, the flavor, the habit.
Friends of mine that have switched from smoking cigarettes to vaping e-juice have reported an increase in cardiovascular capacity; but as a non-smoker that started vaping, I definitely noticed decreased performance.
At super low power it's pretty much totally safe and the impact on breathing is temporary[1]. At ~>18 watts formaldehyde starts to become a possible irritant, and there are also lots of other carbonyls. One of the really fun ones in the graph in [1] is acrolein- it's still at extremely low levels but that shit is not anything you want in your body. It's generated in small amounts any time anything fatty is burned, but absorbing it through your lungs daily is a totally different thing.
Vaping at low power (<20 watts) is pretty safe, but my girlfriends vape goes up to 200 and she uses it constantly at 85 or so. There are definitely significant amounts of chemicals besides glycerine and propylene glycol.
[1]: https://monq.com/vg/
This is why I really wish someone would sell an ultrasonic vape, which the original patent included. That should be far safer, but so far, nobody seems to be making them.
Kanthal requires a very specific heating profile after installation to develop its protective coating. Without that its basically just weird, fancy stainless steel. It becomes very brittle after the heat treat which causes gradual degradation especially during repeated, fast heating cycles. I would not use it.
I would also avoid low-alloy stainless like 400 series. That's the cheapest kind and at elevated temperature it oxidizes and corrodes. 300 series would be better, 500 would be best. Even within those two series though, some alloys will be much better than others.
Nickel... I don't know. It's very sensitive to composition and some can leach into liquid and others don't. It's more toxic than iron or chromium, but pretty resistant to temperature. Kind of a wash.
Cigar and pipe smokers as a rule don't have the kind of compulsive many a day habits that cigarette smokers do.
[1] https://en.wikipedia.org/wiki/Tobacco-specific_nitrosamines
http://www.medicinenet.com/smokeless_tobacco/article.htm
To me it's unclear whether or not nicotine itself is actually bad.
I don't think it takes a huge leap to realize inhaling smoke is not good for you.