Asa former vape store employee and enthusiast, here’s my two cents… The ‘unregulated’ stuff is general WAY cleaner than the stuff the fda and big tobacco get their hands on. From what I heard, juuls and other pod based systems had massive amounts of nicotine and unknown ingredients. 48mg of nicotine was considered incredibly high when I worked and the only people that used it were people that were extremely addicted, case a day or more, non-filter type smokers, and we sold it with great caution. I forget the exact number but the amount of nicotine in juul puds was more than 48mg, and kids were using these things before they were even 18, being non smokers and getting addicted to nicotine. I’m usually super against regulations like this, but the juul craze was dangerous.
As far as the other ‘unregulated’ juices… We made our own juices, in the shop, to order. The ingredients were simply four things… propylene glycol (commonly pumped into hvac systems for sterilization in hospitals before hepa filters existed), vegetable glycerin (common ingredient in foods and topical creams, cosmetics etc, fda approved food grade flavorings), and pure nicotine.