They have a clip-on to the glasses that convert from AR to VR mode. So you wouldn't need a reflective surface portal as you say. I believe switching between the two headsets would just be a matter of software. I'm wondering if that support exists or is easy to make, or whether there would be difficult challenges to it.

Basically, I'd prefer to buy one system that could be both AR and VR than two separate systems, one for VR and one for AR. So that would make CastAR beat out Oculus Rift unless the Oculus Rift was just so much better or the software was incompatible.