I started using the iPhone with the 3G and never had a screen protector until the iPhone 6. I’m not a frequent dropper, but I do drop my iPhone every now and then. Only once, on a driveway with lots of large pebbles embedded in the concrete, did that screen protector break. I removed the shattered protector and found a completely undamaged display underneath, so I’m glad I had it. Will I put one on my X? Probably. I used to hate the sticky film protectors some people would get for their smartphones and PDA’s, but the tempered glass protectors I’ve seen are so clear it’s hard to tell they are there. They work fine with 3D Touch as well. I’m sure there are some protectors that aren’t as good as others, so YMMV.
I don’t use any protection for my Apple Watch, and after more than two years it still looks new.
A $30 or $40 protector like the Zagg might be better made than most $10 products, but there are some $10 ones that get good reviews. 10 bucks isn’t much to pay for a little peace of mind. If you don’t like it, you can always remove it.