Why not use OPNsense on a mini PC?
The Omnia NG is fanless, meaning quiet and power-efficient. It's also small and relatively stylish. The small hardware LCD is very handy, and everything Just Works. The whole package is just so well put together.
I mean is it supported by vanilla OpenWRT image?
I do like the board though.
There are even people who have gotten NixOS running on it, apparently.