I ordered one piece of 56G QSFP+ passive copper cable for my switch to server connection. For the quality of the low cost copper cable, I think it can be rated as a high level. Its working performance is as I have expected.

I tried FS 56G cable on my Mellanox switch. I was a little worried about the quality in the beginning, but when I inserted it to the switch, vendor name and serial number appears in the port summary, link is up. No issue so far.
The only concerns is about the delivery time, since it is not in stock, I wait for some days. Hope there will be some stock in USA later.