Brand new owner of a Kobo Aura One and thought I'd post my initial thoughts.
I really like the reader--I don't detect any faults pinholes/gradients in the screen--so either I have a near perfect screen or my eyesight is bad enough that I don't notice the imperfections. Either way I'm happy
Text is much crisper than my Aura HD--and I love the larger screen size.
I've only had the One for a little over 24 hours now, but so far haven't noticed any battery drain problems--currently it's at 92% after one day of charging and reading for about 45 minutes. Totally acceptable. It's running the latest firmware--and I know that has fixed battery issues for a lot of people. Also, I'm not currently using a sleep cover but I do have one on order from Amazon, so that may affect things a little.
The minor quibble I have so far is the lighting--the light is much much brighter on my Aura One than on any of my other lighted readers. 10% brightness on my Aura One is comparable to about 35%-40% brightness on my Aura HD. I'm not sure how I feel about the "Natural Light" feature either--the nighttime mode is way too "orange" for me. I ended up turning the "auto" feature off for both brightness and natural light. It wasn't working well at all--adjusting up and down constantly with no change in the external lighting. Very distracting. Also regarding the lighting--I find the adjustments to finicky. I had a hard time manually adjusting to a light level low enough to be comfortable reading in bed. It seems that the adjustment goes by 0% from 1% to 5% then goes in 5% increments. 5% is a little too dim and 10% a little to bright. I'll have to take a look at the available patches to see if there is something I can use there to allow finer adjustments to the brightness level.
Even at 0% the reader emits some light--but that being said when I was attempting to adjust the lighting to a comfortable level last night I did get somehow get the light to turn off completely a few times--had to use the upswipe on the left side of the screen to turn the light back on to see what I was doing. Swiping to change the light level works better on my HD--I find it to be inconsistent on the One. The firmware version may have something to do with that. I'm still running an older firmware on my HD--I think it's 3.15, but the One is running the latest version.
All and all--I really like the Kobo Aura One--for any of you trying to decide whether you should get one, I say do it!