I had the NJoy mini cigarette looking one.. The cartridge in it is (or was) TINY and it's very easy to end up vaping a dry atomizer. When you vape something dry it'll burn and hurt. The only way I ever got decent performance was to drop liquid directly onto the atomizer.. I couldn't always get the atomizers to last, either, but some of them were surprisingly durable and the lady at NJoy was very nice about sending replacements. The batteries were good for being a miniature device. .
I don't think NJoy cartomizers are any good.. the ones that come in a bottle... I don't think they are. Never tried them because never heard anything good about 'em.
I never had a problem with their juice being harsh but like everyone says I've definitely heard many times that certain people are sensitive to PG. I've only had juice that was harsh one time - was a cheap dekang "pina colada" that tasted horrible and burned the piss out of me!!! (I vape their other flavors without issue) But it was vapeable if I would draw vapor into my mouth and french inhale it (for some reason)
After you've been away from smoking for awhile you'll have some symptoms as the lungs clean themselves and nerve endings grow back in the throat. It's a great experience, detoxifying.. The years of the built up marinade of chemicals will be leeching out of your gums for awhile, so you might want to carry extra mints and brush your teeth more often..
That is what smokers cough is, smoking kills the little cleaning hairs in the lungs, so smokers are constantly coughing themselves to death trying to bring up all of that tar and junk and 90% of it just will not come out. Once they start coming back (if you're lucky enough that they do, and I think most people are) you will be able to bring up all of the tar and that won't last forever