Just a heads up. Nexus 4 has gorilla glass on front and back. Thats not to say its completely scratch proof, but it should be a lot more scratch resistant than a typical handset screen.
Another note, I ordered from Screen Guardz before for a tablet screen cover. They did end up shipping me a cover for the wrong device, but promptly sent out the correct one when I contacted them. Not a big issue, just had to wait a bit longer than expected.
Been hanging at XDA forums and lots of people are complaining of scratches on their handsets, some even got them out of the box. You really want to protect this as soon as possible.