Nice write-up. A few points.
1. I would make a clearer distinction between "carts" and the filler material itself. The cartridge can be used indefinitely, but the filler material cannot. The car is the hard plastic shell while the filler material is typically polyester batting stuffed inside.
2. I would disagree about throat hit and vapor production. My DSE-601 e-Pipe and Ruyan e-cigar have fantastic vapor production but no throat hit. I think this may have more to do with the temperature of the vapor itself and the contents of the vapor.
3. PG is not glycerin. PG is made by the reaction of propylene oxide and water. It metabolizes in the body as lactic acid not glucose like VG would. Glycerin, however, can be made from either plant or animal. PG can cause some reactions in people such as itching and sore throat while VG tends to have less adverse reactions for those with PG issues. VG is much easier to find in stores for those looking to make their own juices.
Remember that one?
I'm sure you've learned much more since then.
In 1 - A cart lasts how long?... It's plastic. I assure you it doesn't last indefinitely.
In 2 - Generally speaking... you nailed it! It does need to be incorporated into the OP.
--- ignore the below, I'm just talking to hear myself talk ---
In 3 - Propylene glycol is an organic compound. It is metabolized in the human body into pyruvic acid, which is a normal part of the glucose metabolism process and is readily converted to energy. Yes, this may include a reduced lactic acid conversion, but I'm not so sure this process happens from inhaling PG vapors since alot of oxygen is present in the pathway. We need more study on the human impact of PG vapors. I think we can at least say we are inhaling a germicide vapor. IDK, have you had a cold yet?
Vegetable Glycerin is a glycerol. In humans and other mammals glycerol is sometimes not considered a true gluconeogenic substrate, as it cannot be used to generate new glucose. It's true in alot of other animals, but not always true with mammals. VG is extracted using high heat and pressure and the temperatures can reach more than 400 degrees F. during the process. This process already decomposes the VG a fair amount and so another reheat process (say the heat from a HV mod atomizer) is sufficient to decompose it some more and possibly create a trace of acrolein. The same thing applies here as well... We need more study on the human impact of VG vapors. IDK, has anyone got an acrid smell yet? I think it would be safe to say you should only use VG in a standard Low Volt setup and only vape in 5 second intervals.
Water-based USP PG is the ideal ingredient to use as a clean delivery of nicotine fog. Yes, some people find they are allergic to it and have no other choice but to switch to a VG or RPG [Reduced PG] liquid. If you're allergic to mouthwash, toothpaste, cosmetics, foods, fog machine vapor, and other items because they have PG in them, then you should suspect some allergic reaction to PG-based e-liquid too. Just use caution and be prepared, but don't freak out. There is a possibility your body can adapt to the PG vapors and eliminate any allergic reactions. We just don't know about these things. We need more study!
One thing is for sure... If you can survive smoking tobacco and it's 4,000+ chemical counterparts, then vaping e-liquid should be a walk in the park for you.
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One other thing that could be added to the OP primer (not sure if it's already been mentioned, I was too lazy to read all of the posts)...
The nicotine levels you find on the e-liquids are measure in mg/ml, that is for every ml of volume there is X mg of nicotine in it. Yes, it sounds incredibly high at first, but you'll soon realize it's not the same as naturally occuring nicotine.
Here's a good scale to go by, but remember not all e-liquid is created equal. This is relative to what type of cigarette you were/are smoking:
24 mg/ml = a non-filter brand
18 mg/ml = a full-flavored filtered brand
12 mg/ml = a light filtered brand
6 mg/ml = an ultra-light filtered brand
0 mg/ml = your sucking on an unlit cigarette
There are higher concentrations right now, but they're mostly intended for cutting and mixing your own recipes. Future regulation will change all of this, but I have no idea where the line will be drawn.