I have used a low power Qotom Intel-based mini pc with 4 NICs running Opnsense since version 18.x. I bought it off Amazon for 300 USD and it runs like a charm. It currently serves my 1Gbps fibre connection with significant amount of simultaneous workloads without a sweat. Only downside is in the older models the Qotom bios will not get past POST if no screen is plugged in, so you will need either a screen when you reboot or a stump VGA cable with a resistor built in. Apart from this, I can highly recommend it.