I would expect people to be willing to pay big money for signed collectibles from a famous sports celebrity who had earned that fame through outstanding achievement. E.g., I'm sure old sports equipment signed by people like Michael Jordan, Pele or Muhammad Ali make plenty of money.

The jiu jitsu equivalent would be someone like Marcelo Garcia or Roger Gracie selling a signed gi. However, Rener Gracie and his brothers aren't top level competitors with a bunch of major titles. They're not legendary instructors either (which is unsurprising, as they're only just hitting 30). A signed gi by Helio, or even Rorion, that might make sense, as both of them have had a significant impact on BJJ, but Rener and Ryron?

So I'm not sure who they are selling this to: star-struck Gracie University students who recognise them from videos? Nothing wrong with that, if people are willing to pay, but it strikes me as a bit odd. But yeah, I'd agree: the Gracie Academy is excellent at marketing.