Key point that this glossed over: because this drug targets the protein amyloid, it is only really effective before the point that amyloid reaches a critical level. Once this happens (the exact point is still unknown), other changes occur which leads to permanent brain damage. The drug will then no longer work to prevent the disease.
This article states that amyloid PET (brain scans to detect presence of abnormal amyloid early) is not covered by insurance, but there are new blood tests that may perform as well. My lab is working on validating these blood tests. Keep an eye on new studies being released next week on the 16th, which is the first day of the annual Alzheimers Association conference