Eh, what's that all about?
There's no particular reason I know of for a USB-based NIC/SATA/whatever to be a CPU hog in any way.

USB gizmos are packet-based DMA devices on a fairly high-speed (USB3) bus. "Register" accesses can be expensive time-wise, but not CPU-wise, and there's generally no need for those "on the fly" anyway.

I've got some $10 GigE USB2 NICs here that work very well (30+MBytes/sec throughput) with older machines lacking internal GigE ports.

-ml