They are very different types of glass Screen protectors don't provide any drop protection, they are meant for preventing scratches. Screen protectors usually scratch and break so easily so saying "wow the screen protector cracked sacrificing itself to save the screen" is like saying "wow a book fell and hit me in the head but fortunately I was wearing a hat and an egg under the hat, the egg cracked and saved my life" in reality, nothing would have really happened to your skull if you didn't have an egg under your hat. A properly designed case a different story, there are some cases that are specifically designed for drop protection and they do act like a helmet, a helmet can save your life, an egg won't.