I have to say the K6 I got on Black Friday sale is just so cute. I love it. Perfect size for reading.
I am using it without a case and I have never used screen protectors on any of my devices. I'd be worried about the glue on my nice screen and also, there is no way I could that that thing on straight enough to make me happy. I remember the drama when I put a skin on my kindle keyboard years ago. Holy moly that took forever. My hands shake too much for that.
I would also worry about it getting blurry with another layer on it.
I got it cheap enough that I don't have to worry. I mean really, I never scratched the screen of any of my devices, including the expensive K1 I have had since 2008.
I think it also hinders my touch screen abilities. I am one of those touch screen challenged folks. I can't explain it. It just is.
I was surprised though at how heavy the little Fire feels. Its so spiffy though. I have the very first Fire, the original one and a 2012 8.9. This little thing is so snappy. And I love how the kindle app looks and the features. I like it more than the android app on my Nexus. Smoother. Of course its integrated so that's probably it.
Feels really sturdy too.