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.
You can:
(a) Remove all sd cards and turn on the device. It should enter a special MASKROM mode where using a USB 3.0 Type A to Type A cable you can use RKDevTool to flash the special bootloader to do this. I didn't have much success doing this - my computer just wouldn't recognise that the device was plugged in.
(b) Boot into any compatible image (Radxa official image is the easiest) and use rsetup to flash the SPI bootloader.
The device ships without a heatsink or fan but there is a supplied fan header. The CPU regularly will exceed 60C when run without a heatsink or fan and its is strongly recommended to install a heatsink or fan unless you are using it for low power uses.