I'm not sure on the benefits...does the documentation say how fast the USB connection is?
Ethernet is 10/100Mbps, but I don't know what USB is. NTL always seem to get newcomers to use their USB port for some reason and I'd like to know why. I have always used Ethernet/NIC/Lan cards, or whatever you like to call them.
Usually to change to Ethernet you have to phone NTL and get them to re-assign your MAC address to your Ethernet card. Basically switch your box off, plug it into your ethernet card, via a CAT 5 UTP cable, phone NTL and tell them what you wanna do. They will take you through it very easily. It's pretty straightforward.
You don't need to go through the whole NTL disc setup either. Just enter your DNS numbers into the Network Properties section in the control panel and away you go. As long as you get NTL to re-assign the MAC address to your ethernet cards IP.