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I've used them before. They are great for about a month. They strech out and break at weak points in the silicone. Let's dirt and other particles into the case that can scratch the iPhone. I'd say go for the incase slider in black. It has a really cool texture and protects well.

I also use a screen protector, you kind of have to get it just perfect for the screen protector and the slider case to fit well together. Try differnt brands of protectors and I've also heard of people filing the slider down a little bit and are then able to use any screen protector.
 
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