Some more details:
Ethernet is 100 Mbps (hardware).
I have been struggling at first with armbian booting to a blank colored screen, with random color (pink, light blue, whatever). Turns out, my power supply cable was faulty and the ground connection was interrupted. This created an awkward situation where the power was circulating through the ground of the HDMI connection. Surprisingly this worked for the first stages of booting but soon would trigger the blank screen (I guess at the loading of the kernel framebuffer).
as it should be known by reading the installation guides on the forum, the installation to eMMC must be done with the dedicated script, and not through armbian config; in the latter case, the device will be bricked. Of course I learned that the hard way. In my experience, re-flashing the original firmware via USB did not work, but it worked through the SD card. Hunting down the original Android image can be challenging as most links are dead/expired.
I am attaching a `sbc-bench` run.
The device is slow-ish but possibly usable for light tasks. Still, I think it's amazing I could salvage it, so thanks to the armbian community!
leelbox-s1.txt