it's actually illegal for supplement companies to make anything that resembles a health claim about their own products, even if it's demonstratively true.

Absolutely false. It is completely legal to make the claim as long as you demonstrate that it's true to the FDA and they accept your data. If the benefit were actually present, they could file safety & efficacy data with the FDA and on approval legally make the claim. The fact that they don't tells me that there isn't any benefit worth noting.