I know, it seems like a really simple product and a lot of people initially say, "how can I justify spending $30 on a piece of glass?" Let me tell you, this is simply one of those "must have" items that all of us old pros use and here's why: First of all, it's not just a piece of glass. The people who make this have put a lot of time into designing the glass, specifically with the different layers that make up the whole product. It's designed so it doesn't affect the image you're seeing on the screen at all, while providing more protection that literally any other type of protector.
DO NOT buy the cheap clip on things... the image quality of the LCD screen will suck horribly and you WILL get dust, lint, dirt, and everything else behind the plastic. After you have to keep taking it off to clean it, you start scratching the plastic and before you know it, it looks like crap. This glass screen protector doesn't have this limitation. The main reason I use it is to protect the screen from getting cracked if the camera falls around in the field, something bumps it, etc., and most importantly, to protect my RESALE VALUE. Good luck selling your camera if the LCD screen is all scratched up. People are finicky about that (you're here looking at this page, aren't you?) and it tells the buyer that you didn't take good care of your camera.
Anyway, just buy this thing and you'll see for yourself why we swear by them. Oh, and in case you put it on a little crooked, don't worry. If you use a hairdryer to carefully heat the screen protector a bit, you can use your thumbs with light pressure to move the glass into the perfect position. When it cools back down, it'll be locked in the new position. Taking it off permanently in order to replace it is done in the same manner. No residue is left behind, at least not in the couple times I've done it over the years. Hope this helps in your decision.