This comes well packaged with cleaning materials and instructions. Fitting is easy, take your time and make sure everything is clean.
In normal conditions the screen is just as readable as it was without the protector fitted - you really wouldn't know it was there. In bright sunshine, though, there is some increase in reflectivity, enough that you have to turn away from the light to see the screen comfortably.
I found a small but noticeable loss in touch sensitivity towards the edges of the screen, in about the outside centimetre. It doesn't make the phone unusable, far from it, but for example the Home button requires a distinct tap rather then just a touch. The inner part of the screen is unaffected and the feel is as smooth as the original screen.
It is reassuring knowing that, if the worst happens, you stand a good chance of just replacing the protector instead of an expensive repair, and much of the time you won't even notice the protector is fitted. If you use the phone a lot as a tablet, as I do, then you might notice differences in touch and reflectivity. It doesn't spoil the phone, it just takes the edge off the experience of using it a little. Whether that's worth the reassurance only you can decide.
In the end, I decided to remove the protector and see whether I was imagining the effects: I wasn't, the improvement in touch and reflectivity without the protector was small, but it was there. For now I have left it off, but I may change my mind. For what it's worth, removing the protector was as easy as applying it: just put a fingernail under a corner and lift very gently, and the protector will slowly unpeel itself from the screen. There are no marks or residue left behind.
This is a good product, but there are drawbacks. If you value the reassurance it offers then I'd say it's well worth a try. You might not even notice the things that bothered me.