Enttec Artnet boxes for DMX to Artnet work great. This is what I have always used. The web interface is a bit of a pain. In most cases, I just leave the box in its default mode for DMX in to Catalyst.

When I need to drive DMX out for LEDs, I use Luminex boxes if I can get them and have had no issue with the Node8s.

After having some issues with other assorted USB devices, I have to agree with Richard that they are not worth the risk of reliability when staying in Artnet works fine.