There is nothing like Novamin among other toothpaste brands. Novamin has long existed as a bone regeneration treatment, with a very proven mode of action. The inventor spun it off and GSK bought the company and made it exclusive to Sensodyne. This isn't a company that made some fun name on a method of fluoride.
It doesn't exist formally in the US (or at least it didn't) because FDA rules would make it fall under a medical treatment and a toothpaste isn't possibly worth the process and bureaucratic overhead.
>Anyway, it doesn't seem like Novamin makes a real difference
That is a study of studies, and its conclusion isn't that there is no "real difference", but that there is a need for more clinical trials, which is an enormous difference.
Because there is little demonstrated proof of Novamin specifically in regards to teeth. It is largely theoretical.
But for what it's worth, I've used it for a bit over a year and now have zero sensitivity and my teeth are demonstratably much whiter. My own anecdotal experience is very positive, though maybe I'll have throat cancer or a third eye or something eventually.