The most expandable x86 single-board computer. Says so on the box.

Sysinfo hangs at the vga bit near the end, hope you don't mind missing
/mnt/apm/ctl...

USB and USB-C: works
HDMI: works with VESA. Realemu gets native res, though I can recall
having to run it manually before or something. No help from CSM, the
one time I legacy-booted. Looking at the sysinfo, it gets native res
right off the bat, I *think* every time this has happened was when I
booted from USB.
SATA works
Ethernet: works
SD card reader: doesn't work on mine in any OS, even though it shows
in Device Manager, lsusb, and usb/ctl. USB2, so it should work, and be
bootable. (Yes, that actually needs to be said, because on some
systems the card reader is SuperSpeed-*only*. On that note,
nitrocaster's T25 is for sale)

Audio: works
On-board Arduino: Doesn't even power on. Shorting RST to GND doesn't
help. Rebooting to Linux and it works (emits "%d\n", n++ over USB
serial on button push).
UART header: doesn't work when those pins are set to UART (instead of
GPIO) in the EFI. CSM doesn't translate to PC-compatible COM port (I
think it's supposed to).

eMMC: Shows up in /dev, doesn't work. With legacy boot, IRQ out of
range and doesn't show up in pci. But in any case, doesn't work. Could
still get some Plan 9-related use out of it, like putting iPXE in it.

PXE booting: legacy boot only. There isn't an discrete option for it
like in a ThinkPad BIOS; you PXE boot by disabling all other booting.
You can EFI PXE boot using iPXE.

WLAN and bluetooth: doesn't work

Random stuff: Bluetooth can be over USB or over UART - a setting in
the EFI. Linux finds four UARTs, the one it calls ttyS0 is the one on
the 40-pin header, I don't know what the others are.

Nicht so geil:
Power button easy to press accidentally.
People on the official product forum are saying the very nice case you
can get for it causes the audio jack to not plug in all the way.
I don't think the B-key has PCIe lanes: it's not advertised as supporting NVMe.
I don't think the m.2's USBs are bootable.

So yeah, pretty good.