One of the main selling points of Purigen is that it's not carbon. It hasn't been shown to cause head and lateral line disease like carbon has. It also tends to turn different colors depending on what it removes. Not exactly an indicator like on a Polypad, but I'd speculate in functions closer to that than to carbon. Purigen is more reusable than carbon too. Or at least far easier to reuse.
You're just not going to find a lot of scientific data from a private chemical company in an industry where ingredients don't need to be disclosed. Not just the aquarium industry. These companies do lots of testing but they keep the data for their own competitive advantage. It would suck to spend lots of money on research just for another company to copy the product without this investment. What we could see is hobbyists conduct studies but they won't really say what in the product is doing this. BRS tends to do studies like these, which are definitely helpful to the community.
I know a former R&D person from Seachem. They really do put a lot of care into their products. I don't think you'll find anyone here that thinks Purigen doesn't pull stuff out. Comparing performance to carbon though, is fair to question. It may even depend on the carbon type/shape they used.
My issue with Seachem is how they treat their workers. It's something I sometimes consider when purchasing, but you know. I'm probably still going to buy Prime when I need a water conditioner. Just my 2 cents.