These tests are more or less useless because there's no treatment anyway so knowing about it a long time in advance will not lead to any substantial gain. Even slowing the disease isn't within the realm of today's technology. Today's pharmaceutical companies are close to quacks as far as Alzheimer is concerned. We know next to nothing about its origins or even how the disease progresses.
The only thing you gain is giving people more time to worry and despair.
The only thing you gain is giving people more time to worry and despair.