It's a two layer board with no attempts made to keep loop areas small, it's going to be bad. Most of what I read of this seems fine at a glance but that part about EMI sticks out as complete nonsense.
Edit: I have nothing against it being a two layer stackup as part of the art of it, I however don't like that they're also claiming that it's designed to have extremely low radiated emissions while doing so.
That is not correct, with a charitable reading of the text. Which is not to say it’ll have good EMI characteristics - you never really know until you get it tested.
> Artificially confining ourselves to two layers is exactly the kind of challenge I am wont to be engulfed by. The trick, if you want the board to work well, is to work on only one layer, and keep almost the entirety of the other layer as ground. It is almost always possible to do this, if you're willing to put in enough thought. I rather find that designing circuit boards is a lot like Tetris, and once I'm in the swing of it I can route things for hours on end. It can become a multi-day trance, with dreams of signal integrity and current loop area.
Though on this subject:
> In contrast, said this one PCB designer, a thin track has a higher inductance, so if you make your power supply lines thin, you'll get a free bit of extra filtering.
Inductance in your power supply lines is bad, but I don’t have time to get into it right now.
> you never really know until you get it tested.
I suspect they haven't given the lack of a CE marking on the board.
As an aside that bothers me a bit given that they say they sold 1000 of the last version, which would easily cover the cost of the (legally required) testing. Normally I'm of the opinion that it's fine to ignore it for some obscure hobby product where the cost of testing would be higher than any expected profits, but in this case they have the money from previous versions of the same product.
[0]: https://mitxela.com/img/uploads/clock/mk4/kicad-screenshot2....
Not always. You want to have appropriate nearby bypass capacitance, but it's common to filter power lines by deliberately adding inductance into them (this also requires care to avoid setting up resonances, but a thin trace will also add some resistance which helps with that). Either way it's not likely to make a detectable difference on this kind of PCB anyway.
The highest energy part of the device is going to be the LEDs, which are switching well below the bottom of the standard EMI compliance range (10Mhz).