A friend of mine was asking my opinion on screen protectors earlier, and I thought it was a topic worth spending more time on than could be expressed in a Facebook comment. Some background info: I hate using cases on my iPhone. I don't like that they add bulk to the phone. The only ones that minimize the added bulk are the ones that really don't offer any significant protection, and thus serve no purpose. And on top of that, the iPhone 4/4S is a beautifully designed device, and covering it up is a waste. When I did use a case, I was always struck by how great the iPhone felt in my hand when I took the case off. So I abandoned the idea altogether.
But I still wanted to keep my iPhone free of scratches, so I decided a screen protector was the way to go. I've used a lot of different screen protectors on a lot of different devices. The worst part about most of them was that although they usually came in packs of three or five, you had to use most of them as "practice" because if you screwed up putting it on you were stuck with bubbles, trapped dust, or even fingerprints permanently stuck against the screen.
For my iPhone 4, I opted to go with the InvisibleShield from ZAGG. They're a little bit pricier than most screen protectors, even despite that you only get a single one (or one for the front of the phone and one for the back), but are backed with a lifetime guarantee, which is great for a few reasons I'll get in to.
But what caught my eye was the application process. Unlike most screen protectors, where you simply peel off the backing and attempt to stick it on the device, the InvisibleShields come with a spray-on solution which is applied to the shield and the device. Because of this, you can adjust and reposition the shield after placing it on the device before actually squeegeeing out the extra solution, which means that as long as you're careful, you can be sure you'll apply it just right the first time.
A side effect of this was that the edges of the shield around the screen tended to be a little bit sticky, which would cause them to accumulate lint or dust over time, which was less than ideal. Because of this, if I had to stick my phone into a particularly tight jeans pocket or something, the InvisibleShield would occasionally get caught and peeled off of the phone. This was annoying, of course, but under the lifetime guarantee I could get a replacement shield whenever I needed for only a few extra dollars to cover shipping. It only happened every few months, but it was still somewhat obnoxious. On the other hand, it meant getting a brand new shield.
A lot of people complain about the texture of the InvisibleShields. Certainly, they're not as nice as using your finger directly on the glass. The shield adds a somewhat "rubbery" texture to the screen, which typically added a bit of friction for my finger, making sliding gestures a bit harder to perform. But as long as it was kept clean, it wasn't particularly noticeable. That being said, it felt like I had to work a lot harder to keep the shield clean than I do with the glass screen.
Issues aside, the InvisibleShields always did a stand-up job of protecting my iPhone from scratches, and they never affected the clarity, color, or sensitivity of the touchscreen. They never got damaged except when they would accidentally peel off, and as I said, getting a replacement was simple.
This might seem like a fairly negative review, but the InvisibleShield is definitely the best screen protector I've ever used. Many other screen protectors will get scratched themselves, making your phone look even worse than if you had just left it without a protector at all. InvisibleShields stay clean right up until they day you get a replacement. I decided that for me, no screen protector was better than keeping my iPhone naked, but the day I decide I need a new case or screen protector, I'm getting an InvisibleShield without question.