My Kobo Aura One arrived this afternoon. Needless to say, I'm very satisfied.
I'm happy to report that my unit came with no screen imperfections and the frontlight uniformity is great. There are some small build quality issues, though.
The right bezel has a little gap between the display and the plastic edge. It's not very noticeable, but it's definitely there. When turning the device on the little square LED at the top right corner causes small light leakage where the gap is. It's not noticeable in daylight, but in complete darkness, a very small dot of light can be seen inside of the gap. The LED light is on only when turning the device on or off, so this in my opinion is not a big deal.
Also, when the frontlight is on, I can see a tiny bit of light coming through the sides of the USB port. It's not visible at all in regular usage, but tilting the device just right while looking inside the USB port reveals minor light leakage spots. I just hope these little imperfections don't affect the waterproof rating in any way.
As I mentioned earlier, the display is pretty much perfect and the frontlight uniformity is great even when using the natural light feature. It's just as sharp if not sharper than my Paperwhite 3 and it appears to have slightly better contrast, as well. It feels wrong going back to reading on a 6" device after spending 5 hours with the Aura One.
I can finally use a large font and still be able to fit ~30 lines of text on the screen.
As for the software, it definitely needs some work. Epubs feel a little slow and my device froze up on one occasion forcing me to restart the device. This shouldn't be happening on a $230 ereader.
The build quality is decent other than the minor light leakage I mentioned earlier. There's no creaking and bending and the device feels very sturdy overall. It's very thin, maybe even too thin for my liking. I'd much rather have a slightly thicker device with a larger battery.
Battery life seems good, not great, just good. Reading exactly 2.5 hours (light at 7%, natural light at 0%, wifi and sync off) caused the battery indicator to go from 100% down to 91%. Keep in mind that the battery has only gone through one charge cycle.
A picture of my Aura One:
http://imgur.com/HUqLpFP