From your link above; "Freebase nicotine has high alkalinity, with a pH of between 7 or 8. The pH level is directly related to how harsh the nicotine is and also the severity of the side effects when vaping. To put it simply, the higher the pH, the harsher the vape."
7 is Neutral, like tap water. Most pool water is between 7-8 pH.
Remember: pH is reported in "logarithmic units". Each number represents a 10-fold change. Water with a pH of 5 is ten times more acidic than water having a pH of 6.
IMO, Freebase = pure, Saltbase = adulterated. Manipulating nicotine to make it more palatable is the same slippery slope that gave us the current self extinguishing, chemical smorgasbord (cigarettes) that we are trying to avoid.