They are. It’s just that they’re both relatively extremely expensive over time (though cheaper initially) and the no mixing eventually becomes an issue. That issue wouldn’t even be one if there were more available nic levels and at the higher levels they do work. Just not at the lower ones.
TLDNR: trying to figure out the different measurement systems
Myself I’m already out of the higher levels. As I understand things, the density of pure nicotine, while being a powder, is close to water (something like 1100 or 1011 or something) which would make 5% pretty close to 50 (so about double of a regular cigarette), and I just mixed 5.75ml of 100mg/ml of unprotonated base into a 60ml bottle. Which would be somewhere between 10 and 9, so I'm starting to get past ultralight territory. Trying to do the math on that but failing. What matters though is blood level of nicotine. The various forms of nicotine (so unprotonated and the various salts) each have different bioavailability, plus since there are many kinds of salts, each with a different weight as well it gets kind of complicated.
i dislike the term “salt nic” because it doesn’t say which chemical it is reacted with to make the salt in the first place. They’re all different chemicals and they all behave (and taste) differently.
NACL or table salt, is sodium and chlorine. There are other sodium salts though that are used as road salt in different weather conditions. NACL is just the warmest one. Some of them are poisonous. When I was a landlord I kept some others around for when it got really cold. I had one brand called “heet” that would bite until -30f instead of just -5 like NACL does. It would kill dogs if they walked in it though.