I don't like its orange peel that makes the iphone look like a toy. I just took it off and put on a hard shield and it now looks much better. BUT this isn't your concern, so to just answer your questions:
1. i had no scratches to begin with
2. very easy to install for me, easier than the hard shield that looks better. The tiny bubbles or dust left under the Zagg shield at installation really heals themselves in a few hours.
3. very durable. I got mean the day before taking it off and used my fingernails to scratch the surface and pressed into the shield just for a test. It was not nearly broken. There were some nail prints afterward that healed in no time.
I put on a cheap case over "Zagged" iphone and the front skin peeled along the edges. It wasn't bad at all though. I just don't like the toyish looking it gives, that's it. Other than that, no problems.