I tested putt preview over and over numerous times in practice mode and I concluded that it was pretty useless after all.
The problem is even if you ding a putt with exactly the same power & direction in the idectical position & condition, the result varies due to the margin of error your putter has. The greater the distance is, the worse accuracy gets. (Duh!...)
In my case, I needed a function like putt preview mostly for longer putts over 13-14 feet. But if you still can't make it in the hole 100% even after hitting it exactly the same way as the preview showed, what's the use of it?
Some people might argue that it's still useful to study breaks & dot speed, but you know what?... When you've been playing long enough, your eyes can tell you pretty much the same thing the putt preview does.
So for me, putt preview is futile.