AFAIK there are two mayflash adapters:
The old adapter was two port and used one usb. There is a new one that looks like the wii u one with 4 ports and two usbs but it has a switch between wii u and pc modes. I think mayflash wii u is identical to official and pc is identical to old.
Comparison midway down page
https://es.dolphin-emu.org/blog/2015/01/01/dolphin-progress-report-december-2014/
The old adapter was two port and used one usb. There is a new one that looks like the wii u one with 4 ports and two usbs but it has a switch between wii u and pc modes. I think mayflash wii u is identical to official and pc is identical to old.
Comparison midway down page
https://es.dolphin-emu.org/blog/2015/01/01/dolphin-progress-report-december-2014/