The Igel One has a standard PC Phoenix Award BIOS - hit the DEL key on power-up in order get into the BIOS setup screens.
The (first and second) BIOS boot options are:
There is also a Hard Disk Boot Priority option. This will show the 1GB NANDrive along with any bootable pen drives you may have inserted before rebooting the machine. It is a simple matter to move the pen drive to the top of the list.
I booted Tiny Core 6.4 from a 4GB pen drive without any problems.
As delivered the Igel One booted into Igel's Universal desktop software.