That's a real tough call. Similar to your situation, my grandfather was diagnosed when I was in elementary school. I've always been an anxious person, even as a kid, and I remember learning then that the disease was likely genetic / hereditary which disturbed me quite a bit. Back then, I eased the fears in my own head with the thought of "They've got about fifty years to cure it before it could affect me" (or "I've got [hopefully] at least fifty years before I have to worry about it even if they don't cure it!").
Well, that time is creeping ever closer for me, and there's still no cure. There are times I search for a specific word that's jussst out of reach and I would guess it's nothing, but it does occasionally give me pause.
I wouldn't get the test — right now at this point in my life, anyway.
I think there would be other ramifications as well — how these tests could ultimately play into insurance coverage and a host of other things.
And as @RosemaryF433825 mentioned, how do you reconcile the knowledge of impending Alzheimer's if that's what the test results show? I think it would really inhibit me from accomplishing all that I still hope to.
I appreciate all the research that's gone into it over the years, but it still is unfortunate that we've reached a point where they can tell whether you're going to get it but not how to cure it.