For those curious, these risers have blue and red LEDs on the riser and a red indicator LED on the PCI-E board. After installing all 6, all but one passed the BIOS test on my B250 Mining Expert motherboard. It turned out that the problematic board not only didn't boot, but also didn't have a red LED. I don't think the missing LED is the cause of the problem, but rather a possible problem with soldering the USB connector.