To know what the salt packets contain, you need to read the information leaflet provided.
"Neti-Pot salt" is salt you can get together with a neti-pot or buy separately as a commercial product, which can contain various things:
- Example 1: pharmaceutical grade sodium chloride (99.9%), non-iodized
- Example 2: "pH neutral" and "isotonic" salt (but table salt is also pH neutral and also isotonic if you mix it with a proper amount of water)
- Example 3: sodium chloride (sea salt) + added essential oils
- WebMD: home-made neti-pot saline solution
I've found 4 reviews, all of which say that nasal irrigation with Neti-Pot may be useful for chronic sinusitis and some other conditions in the upper respiratory tract without any significant side effects:
- American Family Physician, 2009
- PeerJ, 2019
- International Journal of Environmental Research and Public Health, 2017
- Cochrane, 2016
I have found no convincing evidence to say that certain "special" salt, which can be expensive, is better than table salt.
Anyway, on Family Practice Notebook they say it's better to use non-iodized salt, because iodine can affect the function of small hair (cilia) in the respiratory tract.