After having a Blackberry candy bar form factor for years that I kept in a hard case, one that had a plastic shield for even the screen, I've not used anything to protect my OE. I do try to keep it safe as best I can but it is just out there vs my BB which was armored to the hilt and was not even a touch screen to boot.
So far I have one very minor scratch on the glass, and it is glass but I can tell it is not very thick, and I can't even find it right now looking at it. I can't even see it when I'm actually using it, only when the screen is unlit and at a certain angle. The glass itself might not be Corning Gorilla Glass but as that video said there are multiple manufacturers of the same type of stuff. Given the OE's cost it would not surprise me to find that it has another manufacturers product but it clearly is some type of hardened glass.
Finally I will say that the surface will get smudged quick. However a few quick wipes on nearly anything that is not the equivalent of sandpaper takes care of that and it's back to work.