This is a great product and a Raspberry Pi competitor (given how much those have risen in price).
The official documentation is not clear about this so I will add some of my own learnings.
The device can boot from a USB SSD or NVME drive. This significantly increases its usefulness because of the poor write endurance of sd cards.
In order to do so you must flash a dedicated SPI bootloader. By default, the device relies on a bootloader which it expects to see on the SD Card - as the tools warn using an SPI bootloader may make recovery more difficult.