I saw this weekend that the M6 is currently rather good supported with Armbian and 6.13 kernel.
Advantages/disadvantages of the M6 over the T6-LTS:
- There is no flashrom and fixed serial usb-to-serial adapter (which I found no problem in hindsight since the emmc can be removed).
- Free choice of wifi (mainly intel ax210, mediatek 7922 or realtek 8822), USB PD power without the hassle of bootup-problems (the connector is not reused for other USB devices).
- The casing is small and holes for the wifi are not predrilled, installing wifi with the ipex connectors is a hassle since they they are not preinstalled and the M2.E ard is a tight fit (the T6 has 4 pre-drilled holes for antennas and much more space).
- Where the T6 uses pcie3x4 the M6 uses pcie2x1 resulting in almost 2W less consumption in idle (for a less speed).
- For use on battery power (car/boat) the 12V connection of the T6 requires an extra DC-DC adapter where the USB-PD of the M6 works easier. The power connection is not reused as USB port, saving the user many problems.
- Sound is uses the same rt5616 and headphone connector as the T6. HDMI-audio is available upstream, but the patch is an early version depending on many other patches (i.e. the posted patch is incomplete in itself). One armbian developer claims it works for him.
- A small item: the leds also work as intended. I was looking at a good way to make use for the user-led though.
For software I found the firmware needs to be recent and the mesa backport was hard to install (read: if you use an M6 do consider to install trixie instead of bookworm, it might be less work).
With the current 6.13.0/1 kernel most options are already present in the kernel (including support for 1920x1080@60Hz screens). Additional the 4K patch seems to be included in the M6 DTB-file (the DTS seems to be wrtitten by Armbian). The M6 boots with the R6C DTB if needed, but with only 1 working USB port, no M2 for wifi and no working leds.
In comparison with the T6-LTS: the T6 has it's DTS included in the upstream kernel.