They work.

First - I chose the supplier "CTDUSA" and they arrived in 8-days, not the longer shipping time indicated by Amazon since they are coming from the U.K.

I stress tested them in two different BMPCC's at both 24fps and 30fps in RAW. Shooting normal scenes, not static lens-cap testing.
I was able to fill the card with one continuous shot, re-format it, and do it again, all with no dropped frame errors.

The cards don't look particular high-end, there is no serial number or other markings on the back like with legitimate SanDisk Extreme Pro cards, and I have only had them for a few days, so there is no way to speak to the long-term durability. But they definitely work.

Get 'em fast!
There appears to be only a couple hundred of them left... at the most.