what exactly is this for? Replaces broken screen glass or what??
What are you asking about?
I would hazard a guess he is talking about the tempered glass screen protectors.
The glass ones are the same concept as the plastic ones, but with better scratch protection and some people have claimed that if you drop your phone, the tempered glass protector will shatter instead of your phone’s glass.
This amazon comment talked me out of one of the hinged cases: “It adds a lot of bulk and weight to the iPhone 4! To give you an idea, it is thicker than two iphone 4’s stacked on top of each other.”
My son loves his hinged case and uses it instead of carrying a wallet.
I use one when we go on vacations and do touristy things. Much easier than carrying a purse.