I fear due to the curved edges people will encounter the same issues as with the s7 edge which is the phone I'm using and gave up on them especially if a case is being used.
8 months into using it and no scratches.
Ill be doing the the same with my s8.
OK they can be a total nightmare as you have to get it right on which one you select, if you plan on going with a nude phone or just putting a skin (sticker type) on it you can go with a glass screen protector that covers the whole front, BUT if you are planning on a case you have to get a case friendly screen protector and the best ones are the ones made by the producer of the case it's self as they will match up the best and you will not run risk of the glass screen protector popping up on you. But the main thing I will recommend is "spend once" which is to buy a good one rather than 4 cheap protectors as it will only taint the experience for you. Have a watch of this video https://www.youtube.com/watch?v=JPA2mXZuXA4&t=335s
I used many type before I settled on one I was happy with on my S7 edge but this time I went with a Otterbox strada case which is a wallet type so not got a protector this time (yet) but if I do it will be one from Otterbox. I could not force myself to buy a cheap case for an expensive phone.
I put my screen protector on as soon as it came out of the box. "ScreenKnight Samsung Galaxy S8 Plus Screen Protector - for Galaxy S8 + - Curved Fit - Front Military shield". I used this for my S7 edge and S6 edge+ before it and works well with the cases I used with all of these. You put this in soapy water and position it by sliding it around, and 'bubbles' dissappear after a day or two. Yes they did on my S8+ and it works perfectly with my Clear View Standing case.