I've been using this mirror for 2 days and really enjoy it. The book said it may take up to 20 minutes to pinpoint my location, but within 2 minutes it had locked on. I now have fewer blind spots (and my car has very few) because the mirror is convex so I can see out of the windows in my back seats. I do think the auto-tint could tint a bit more, it tints just enough where you have a very clear picture at night. I have yet to take it out on the freeway, but that should happen in the coming weeks.
Oh, and as others have said, this thing is big!