The overall quality is very good but it miss some very important information. The design rules are not complete. I still prefer this (my) one (more complete) ;) : https://www.tindie.com/products/sinzu/the-ultimate-pcb-ruler/ By the way, it's look like you copy some parts from this ruler ...
Shipping: it took 3 weeks to receive it from China to France.
I bought the assembled version, which I regret, because the job is not done well. The boards are not aligned well, some angles are visibly not 90 deg. Some edges have gaps. Assembly wires are protruding from the cube. Overall the cube looks beat up. The boards looks fine. My advise would be to buy the individual boards and do the assembly yourself.
It is unclear if the unassembled version means you get bare pcb and some smd components? Or if the pcbs are assembled and you only needs to assemble the cube?
No documentation is provided. You can google WS2812B datasheet, but you have to figure out how the leds are connected, by using trial and error.