I had a screen protector long ago on my first iPhone4 and also on my first BlackBerry Z10. I tried one on my BlackBerry Playbook Tablet also long ago and it just didn't feel/work right. I haven't used a screen protector on any of my devices since. Not the follow on Z10s, the Q10, any of my Samsung Tablets, not now either on my current Samsung A21. I don't think I could ever use a screen protector anymore, but maybe some of them nowadays are really good/clear. I have only experienced a very few slight scratches over the years, but others probably have to use their devices in way more unforgiving scenarios.
Before my first smartphone (the iPhone4), I experienced far more scratches and screen damage for a few of the "feature phones" I had back then.
I am a fan of no screen protector at all and wonder if they are needed at all, given how fast some people cycle through devices and how well screens are made nowadays (and I normally keep my devices longer than most people).