The Express OS is a cut down version, with less features, and is cheaper.
The interface is simplified and you will see fewer options.
Roaming, Captive Portal, NAT and smart-rf would be available.
You can see a few Wing Express training videos here:
https://www.youtube.com/user/MotorolaAirDefensein these videos you will see how simplified the interface is.
It would be good if someone can post a complete side-by-side list of Express and non-Express features. Anyone have that?