USB NIC consumes more CPU. Also if you are trying to use pfSense or another *BSD based router, they don't support the USB NICs very well. I ran that setup for

USB NIC consumes more CPU. Also if you are trying to use pfSense or another *BSD based router, they don't support the USB NICs very well. I ran that setup for a bit and it was dropping packets left and right. After I switched to a Linux kernel all the issues disappeared. The problems are mostly software, not hardware. Also, if you use a hypervisor and your router in a VM with USB pass through. The overhead on the CPU for USB pass through is significant. Better to PCI pass through the entire USB controller. So, there are gotchas and pit falls but they are mostly manageable and avoidable with a bit of understanding. I ran a pi4 + USB NIC as a router for years before switching to proxmox VM based router (still USB NICs). It was fine, the switch was rough until I figured out the issues.