I have the S8+ and the fingerprint scanner location is not as bad as the reviews say. I have medium sized hands and the length to reach up isn't the issue for me. Since I hold the phone with my left, it's harder to get to. If you hold the phone with your right hand, it's much easier.
I've been using the iris scanner a lot more than the fingerprint. I'm really impressed with how fast it is. It feels natural looking at the phone to unlock it. I don't have to remove my glasses (as long as there is no glare on the lens, it will read right away) or position the phone awkwardly straight in front of my face for it to read.
I have yet to try the face unlock feature.