PEG400 is quite expensive now. I bought mine off Amazon for $18/liter. I haven't used it yet because I was saving it for usage with certain herbal extracts. PEG is not ethylene glycol. The "poly" part is an important distinction.
Anyhoo, I hear it has more of a chemical taste to it than PG. The toxcity myth (for those that look, pg and vg are two of the most studied aerosols out there in humans) and the OSHA safety limits are equivalent to wading through a dense cloud 8 hours a day, 5 days a week, so it is myth as far as I've been able to determine. I spend a lot of time implementing processes that expose people to vapors, so I tend to do a LOT of research on these topics. I haven't seen too many studies on peg400 inhalation.
One thing I want to throw out is that a decent amount of pg we inhale is vapor while the vg is an aerosol. The PG is what boils (producing vapor) and that boiling atomizes the VG (thereby making an aerosol), which doesn't boil at vaping temps. So when we look at safety, we need to consider the exposure to vapor as well as the aerosol. I haven't seen a lot of studies on vapor phase pg or anything else we mix with, but, to maximize safety I'd say using AG is probably safer...but this guy ain't getting rid of pg anytime soon nor am I particularly skeered of PEG400, but that is my personal choice after evaluation of the known info.
Ok, main thing I wanted to say is you can still buy peg400, its still used by those who vape herbal extracts, and there is a difference between vapor and aerosol. Beyond that, I'd recommend those in doubt look at the available research and draw you own conclusions.
Sorry, long ramble almost over. Hope it stimulates curiosity and thought about what we are doing when we vape. A lot is not known about what we are doing inhaling these chemical cocktails...but there is a lot of study on aerosols of the main components that we vape. Knowing what is known and what isn't is the duty of someone using this nic delivery method.
I also gotta agree with @TheTinMan1 that we need to own this. We are inhaling a chemical used in antifreeze. We are inhaling components of hair products and artificial sweeteners among many other things. By owning this it demonstrates the power of knowledge versus blissful/willful ignorance. Like vapor vs. aerosol, owning the knowledge is power. Remaining ignorant is a choice. Take your pick, I propose no judgement. We must do both all the time about much more than vaping. But picking what you know and acknowledging what you dont ensures you're always in a position of power. That's scientist 101.
Here ends the sermon.