Open source bios yes, but you still have close source firmware blobs for amd/intel used on those systems. The only way to do this is to make 100% of the hardware.

Also please note, I am using coreboot already on my pcengines router.

Few computers use CoreBoot, and CoreBoot still uses proprietary blobs typically. Normally only libreboot has zero blobs, and they are very rare indeed.

The problem is that their Web interface and firmware in general are not updated (at all). I think it’s even possible for script kiddies to hack into such managed switches, which forms the reasoning behind my comment.

Does your switch produce its Web interface over TLS?

I did realise that, and apologies for my tone earlier.

With that said, this seems to be a slight bias - unless the PCB has some nefarious spy-chip built inside, hardware is hardware, regardless of where it comes from.

I just found the general combination of security - mindedness and cheap Chinese hardware curious / amusing.

I think it can make sense, since there are so often vulnerabilities in consumer router firmware, and because those devices are so common the vulnerabilities are profitable to exploit. Running a BSD-based router on a cheap Chinese PC is likely to be better security for the router’s OS and software itself, even if you don’t know for sure about the firmware on the board (which you don’t with consumer routers either, really). Overall you could still have reduced your attack surface compared to a popular consumer router.