I have to say I never saw a buggy BIOS like this before!
WYSIWG (what you see is what you get)? Forget it!
(BTW: my "Samsung SSD Portable T1 500GB USB 3.0" is significant slower at Acronis True Image using this port (I'm not sure if only with enabled Charging Mode))
Another example, sometime the "3 sec pressing procedure" at the power button works to get the "extended" menu (ESC, F2, F4, F7, F10, F12) at boot, sometimes not...
Also if I press the power button during boot, at the bios-setup or at the boot-menu the nuc doesn't seems to power off (like at windows 7) because there is power at the USB-ports (e.g. I can see it at the usb2.0 hub I use for the HID-dongles)... I have to say I don't like it...
Another story is
AND SO ON...
It is possible to boot from the internal M.2 or 2.5" drives or from external USB or external drive; the option from a SD card is not possible.
Now, if you want to use USB drives at 3.0, it is necessary to reinstall the operating system with UEFI and Legacy options checked. (both). Format the USB drive at GPT then, install the operating system image.
It is possible to disable the Portable Device Charging Mode of the orange USB port:
Go to BIOS>Advanced>Devices>USB and change Portable Device Charging Mode to "Off"
If you want to disable USB power from standby and sleep mode:
Go to BIOS>Advanced>Power>Secondary Power Settings and uncheck the option: "USB S4/S5 Power"
Intel noted random issues with some memories; please do this work around and keep us posted with your findings.
Go to BIOS>Advanced>Performance>Memory> and uncheck the option Round Trip Latency Optimization