What do you know about the Mangosteen fruit and Xanthones?

I'm a chiropractor and I have a patient that has been taking a product call "Xango". Its a juice made from the mangosteen fruit, which I believe is indigenous to certain parts of Asia. It contains Xanthones, which I just found out was the most powerful antioxidant in the world. This product has supposedly done wonders from people suffering from a number of ailments including RA, high BP and fibromyalgia. hundreds of MDs and D.C swear by it. Are you familiar?