previously, I had a one x, so I know how strong the gorilla glass was, and didnt like the hassle of screen protectors, except for how easy and smoothly my fingers would slide on the matte screen covers.
buying the s5, I didnt think I was gonna use any screen protectors. but my brother showed me his spigen glass protector and I was instantly sold.
not because of the scratch protection, but because of the oleophobic coating. this coating makes the screen so much easier to use and slide around on. the stock screen also doesnt work well in a humid place with moisture, like a steamy showered room. the gorilla glass becomes all tacky and hardy to use wih moist or damp fingers.
the spigen screen protector makes it easy to slide around on, and the water on the screen doesnt give false readings to the digitzer like the stock glass does.
the other thing I like a lot about this is that with the cover on, the exposed home button is now flush with the screen, it just feels more comfortable and "normal", especially if you utilize the finger print scanner. I bought the .2mm version.
my brother has the .23mm version, im not sure how the s4 varies in physical specs, but my brother noticed immediately that my screen glass was thinner than his. he also has a little gel sticker insert to raise up his home button to be used with his cover. he opted for the slightly thicker glass for durability purposes.
I am content with having the the thinnest cover because I dont anticipate dropping my phone much, and I already have a sturdy enough case on.
I dont know about other brands, but I am perfectly content and very happy with my purchase. 10/10 on the reccomendations factor.