I finally got around to playing on the deck. I do wish the screen was a little better (only 68% sRGB coverage but you don't really notice it and basically what you get on a cheap laptop), but the matte screen that comes with the 512 is usable for me. I put 13 hours into a standard platformer on the deck's screen. Maybe it would be different with a FPS type game. I don't know if the glossy screen used by the 64/256 models is the same panel or a different one. It's also possible that there's been a panel change because some people have been complaining about bubbles and having to cure the screen with 15 minutes of UV before using it safely (what?) which was not at all the case with earlier shipments.
It is possible to configure the night mode overlay in such a way that it adjusts the colours so it's not so blue, and closer to 6500 kelvin. Night mode does work in games also so it's one setting that you can toggle on and off.
I'll get a dock eventually, will be interesting to see how it is on my monitor.