I would always buy screen protectors and have them in my possession before I even got the actual device, lol. I was incredibly anal about it but not woth my Nexus 7. My N7's screen is naked and i love it like this!
I even have a Zagg Invisible shield on my iPhone which is definitely NOT invisible. Its got a nasty orange-peel effect, feels grippy and sh*tty and attracts dirt and gunk more than the naked screen. If it wasn't for the fact that I throw my iPhone in my pocket, sometimes with keys, I'd pull that crappy screen protector off immediately!
And that's my point: unless you are planning on throwing your N7 in you pocket/bag with keys or other objects that can scratch it, its not necessary to have a screen protector. Or you're letting a child use it, there's no real need for a screen protector in most cases.
I've had two N7's, with daily use that has replaced my two laptops, and I don't have a single scuff, scratch or mark on either of them.
That's not to say down the line I won't revisit the idea of a screen protector for my N7 but currently I don't want one and the ones I've seen are crappy or change the feel of the screen.
Just get a good case with a solid cover and you'll be fine.
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