Summary: I had another usb audio I/O device that I was using for Mixvibes DJ software, but it was only 2 channel, so I did not have a cue channel. I looked at a new controller with built in audio, but it was sold out, so I bought the Numark DJio. I use it for DJ gigs as well as playing music on a live podcast.
Pros: Sounds great and easy to use. Portable.
Cons: Install was a bit of a hassle. It takes a while to install, and I cancelled the install the first 2 times because it locked up the computer. I finally just left it running while I was doing something else, came back, and it was done.
Summary: Very disappointed with this piece of kit. Mainly due to the fact that I use a Mac running Traktor on OS X Leopard and Numark currently doesn't support this. As a result the DJ IO will just stop working after about 20 minutes - not good when you're a mobile DJ with a crowd in front of you. I'd go for the ESI Gigaport AG 8 Channel USB Soundcard instead (http://www.djstore.com/item/esigigaportag.htm).