I had to pay around a thousand usd for a sleep study, and had to see a sleep specialist for a year. He told me I was pretty lucky, if I tried it any longer I could have gotten permanent brain damage. He was suspicious of polyphasic claims, because he often saw people use modafinil in conjunction with this(especially among lawyers).
Maybe some people are genetically predisposed to this form of sleeping, but running experiments on yourself may not be worth it.