I'm not sure if that heavy rake on the front end, (for a production bike anyway), would make it lean into the corners enough to counteract the instability, not to mention what it would be like riding across an incline. I suppose that with the front tires that close together though that it would be an easy matter to rock it up on two wheels and ride it like a bicycle if you needed to really lean. That would probably make for some strange steering behavior though.
I noticed that the video on their site only shows it being ridden on level ground. Yes, they pedal it up stairs, but only head on and they never show it leaning to either side or cornering.