This is a fun one, I considered making one like that myself as well but didn't have the time to, so I'm glad someone else made it real (though it would've been nice if the source files were available). It makes use of the fact that PCIe lanes from the Intel PCH can be reconfigured in firmware (I have an explanation about that
here, though it seems they streamlined the flashing process for this specific adapter and platform).
In this case it's splitting the x4 link into 4 x1 links and using a clock buffer to split the refclk to the 4 slots. That gets you 4 drives running at PCIe 3.0 x1 off of the PCH, so up to just under 1GB/s per drive, and you still have the full PCIe x8 slot from the CPU as well (though with the SSDs installed you won't have much space lol).
It's a pretty cool riser in theory. I haven't seen it in practical use, but I imagine it works just fine. Seems to be using an extra buck converter to run the SSDs off of the beefier 12V rail so there should be no concerns about going over the tiny's onboard 3.3V regulator's limit, it just counts to the maximum total shared with the 12V for the PCIe slot now.