If you hold the phone on the sides and your fingers wrap around does it have a tendency to make 'false hits' (i.e, interact with the touch display) ?
I had a decent amount of false hits with my previous S7 Edge. I have not had the same issues with my S8+ though I'm not sure if it's due to the different edge angles, improved software, or both.
As for fingerprint scanner, you learn to live with it on the S8+ but to me it's a definite downside compared to the phones with a more central location. I simply use 2 hands now whenever I need to use the scanner and with that assumption, it's fast and easy. Most people should just give up on trying to one hand the scanner.
As an aside, I don't think any facial recognition system is a full replacement for a fingerprint scanner but instead can be a great partner. I initially tried to solely use iris scanning and found it tedious to have to hold up to my face. However having it available at certain times is great (wet hands, gloves, etc).