I DIY with nic salts at about 18 mg./ml. I mainly got them because my throat, lungs and everything else were pretty torn up and I wanted something easier on my system. I could probably start vaping regular nic again any old time but for me they were useful to start with.
Reasons people use then: Ultra high nic needs, or because they are the latest and greatest. I really think the former has the most usefulness.
I will say, there are some reports of nic salts being more bioavailable more quickly but now some of those claims are mixed, and indicating they really aren't much different than freebase nicotine. They reportedly store better, for longer. I have some of both nic now, so I guess I will see.
If you want to try them at high concentrations, make sure you delivery device isn't too overpowering for your nic salt concentration, like don't use nic salts in a severly sub0hm device at 50 mg/ml or anything. Although folks with sensitivity to nic also find them useful, I think. You can use them in ANY device, just at the right concentration. Some folks will use them in sub0hm devices at 6 mg/ml if they are ultra sensitive to harshness and etc.
With that said, honestly, they're not magic, special or anything else. All this "nic salt" capable device advertising is just that. Advertising. Anyone can use nic salts at the right strength for their device, although MOST folks using lower nic levels just don't really need them as the nic is low enough to not cause harshness in any case.
Best of luck,
Anna