The USB ports are not usable currently and no timeframe has been published on when they will or even what you can do with them. If you go with the AD2USB you will need a computer on 24x7 to use with it, which is why the AD2Pi + Arduino + ThingShield is much better, but more expensive. I also have been using this for many months now and love it. The project is documented here:
You will see a post from me at the bottom where I add features to Stan’s work by allowing the zones to work independently with more processing on the Arduino.