ugen0: <vendor 0="" 2="" 0x0fe6="" usb="" network="" controller,="" class="" 0,="" rev="" 1.10="" 1.01,="" addr="">on uhub3</vendor>
I bought 2 of these USB-Ethernet units today for an old laptop that I'm using as a pfsense box. They produced the exact same dmesg output as yours in my pfsense 1.2.3 install. So I booted from 2.0 beta (latest snapshot) and they were detected as 10/100 USB ethernet (ue0 and ue0) devices. However, even though they were detected and had connectivity.. the link was limited to USB 1.0 speed (bout 1-1.5mbps max). They also had somewhat increased latency by 1-5ms when I ran a ping test and were quite unstable.
I would not recommend using these USB-Ethernet for pfSense. I'm returning them and getting a proper system with Intel NICs tomorrow.