What is differences in usage between a HC-05 bluetooth module and a Zigbee HC-05 module?
Bluetooth and Zigbee are two different communication protocols. The Xbee clones you are talking about a called BTbee. 

As far as im aware the BTbee modules are the same hardware/firmware wise as the hc05/hc06 modules. The only difference being the BTbee modules are in the Xbee footprint, allowing you to plug them into Xbee/Zigbee sockets.