Nicotine isn't derived from tobacco. Unlike the nicotine typically used in e-liquids, these salts aren't just nicotine; they're compounds containing nicotine and other organic components.
The form of nicotine commonly used in e-liquids is called "freebase," meaning it's unbound from any other substances. It's generally considered suitable for e-cigarette atomization and other purposes because it's a more volatile form.
Nicotine salt e-liquids are primarily designed for low-power devices. They offer a portable design, high resistance, and a firm mouthfeel, allowing users to achieve a realistic smoking experience while still ingesting nicotine.
The biggest advantage for novice e-cigarette users is that they get their nicotine needs faster and without the need for overly complex equipment. They offer a more convenient way to satisfy your nicotine needs than standard e-liquids. However, if you're using a high-power device, nicotine salts containing more than 15mg of nicotine are unsuitable, as they can be very harsh.
In general, the emergence of nicotine salt e-liquid is a novel experience for users, providing those who cannot replace cigarettes with free base nicotine with a most satisfactory alternative.