It's an excellent product, but some of the uses ascribed to it by avid users defy all reason. Also, 303 Aerospace is now a brand name and they package several different products with the label, e.g. a fabric water repellent, a cleaner spray, etc., so don't just grab a bottle with the 303 label on it if you are looking for the original product, 303 Aerospace Protectant. The 303 RV & Marine Protectant appears to be the essentially same product with a different label.
It's main claim to fame is that it is a UV inhibitor, with a SPF 40 rating. That can reduce the impact of sunlight UV on rubber, vinyl, plastic, etc. To the extent that UV is a problem with some surface or material, 303 Protectant can help. Those who are convinced that UV is destroying everything around them often believe that applying 303 has saved them untold expense and worry. As evidence that is so, they proudly display good looking tires, decals, vinyl upholstery, etc. Whether it resulted from the 303 or just their regular tender loving care is maybe another question.
This glowing advertisement on the Autogeek website describes many of its potential applications. I'll leave it to you to determine how credible the claims are.
Personally, I've used 303 Protectant as a tire dressing for cosmetic reasons (cause my tires all last several years anyway) and the Fabric Guard product as a water repellent on awnings and such.
https://www.autogeek.net/303aerprot.html