I used a screen protector only once. I hated the tiny bubbles (Thanks, Don Ho) that were inevitable to get when applying one, so I took it off and never used one again. The one I got came in a pack of five. Four of them are still in a junk drawer somewhere.
The screens that Apple uses are still Corning Gorilla Glass, just a Gorilla Glass that is a proprietary version for Apple that is a bit stronger than Gorilla Glass IV. Recall that when Apple was toying with switching to Sapphire screens that Corning went on a campaign to denigrate sapphire as a screen material claiming that while it may be harder it was actually more brittle than their Gorilla Glass. Apple returned to the Corning fold when only 10% of the 240 pound sapphire boules being produced by Apple's sapphire producer were successfully surviving the long cooling phase without developing disastrous radial cracks, when the contract required at least 80% success to meet production standards.
Apple no longer specifically names Gorilla Glass as a product being used as they did in the earlier iPhone marketing, but Corning is listed among one of Apple's primary suppliers in their supply chain listings for the iPhone, iPad, iPod touch, and MacBooks.
One thing to be careful about is sand. I read that many screens get scratched by ordinary sand that gets into your pockets. So if I'm at the beach, the phone stays in the glove compartment. Who wants to take calls at the beach anyhow? I have a beat up Kindle that I can take on the beach for reading.