I would not use any screen protector that required a permanent adhesive like that. The purpose of a screen protector is to protect the screen from damage and then be removable. If your screen protector is permanently glued to your screen then either you’re not going to be able to get it off and when it scratches it’ll be permanent, or when you try to take it off it’s going to do more damage than if you hadn’t used one at all. Did the people selling it not tell you how to apply it to the device? Sounds fishy to me, I would definitely not glue anything to my iPhone.