I use them as I was looking for LACK of throat hit when I got here. I DIY at about 18 mg/ml, not a crazy amount, and I find they work just as well for me if not better than regular nic. Since I don't smoke any more of it than regular nic, I keep using them as I like the results.
The main benefit is a smoother throat hit. I know they are said to be more quickly bioavailable than the freebase nic that's used, I don't notice that a huge amount. But, I don't vape them any more than I would regular e-liquid so I feel comfortable using them, and I tend to like them. If they are more bioavailable, it's not the hugest effect (at least for me, some other folks might need to monitor their consumption).
Juul gets them to that crazy high level by using a high resistance coil and almost no wattage, so each "puff" is rather small, but some smokers do swear by the Juul, despite price, so they must be working for somebody. I gather Juul is "proprietary" in some way, and some Juul users have a hard time even with other nic salts compared to the Juul. IDK what it is....
Anna