After they were diagnosed, when treatment and monitoring has begun. That makes it 100% effective and only used by people diagnosed with the disease. You take a healthy 35 year old, he's not going to use anything to test himself because he's not sick. If he gets sick, he's not going to use anything to test himself because he cannot self prescribe, even a doctor can't do that. He's going to have to see a doctor, and unless malpractice lawsuits drop significantly, no doc is going to take his word for it, or take the word of the instrument in his home. Eventually said instrument might be hooked into a communication network that's protected privacy laws that only your doctor can use. If that's the case, the doctor could have you scan yourself at home and he could interpret the results, but he's still going to charge you.