Accuracy of the Dreem Headband Compared to a Medical Polisomnograph

“Please take in consideration that device is a FDA medical device class II and has almost the same level of accuracy of a medical polisomnograph (87 %) which costs 15 to 20 times more.” “You have three offers on ebay, a Dreem, a Dreem1 and a Dreem2 headband. What is the difference between these devices? …