You are correct, the finger scan is rendered useless. That's fine for me, we've always used a pass code on our phones anyway, so it was no change.
The dual flash fits perfectly inside the flash opening on both cases with just a little room to spare. I didn't think it would, but I measured it with a caliper, and it's just perfect!
I use the N??d and see no difference in picture quality or dark edges at all. My wife uses the Frē, and is far more photo savvy than I am, and has absolutely no problem with that case either.
The cases fit snug against the back of our phones, and there is no flash bleeding thru around the edges of the cutout on the case. This was a concern for me at first, because my wife's case is Teal.
There was a good deal at the verizon store, and I get a discount on accessories, so we jumped in and got the cases. Best purchase for our phones yet, I've always used LifeProof cases and like their style.