The Samarai Monocopter, developed by Lockheed Martin, is only ten inches long. But the designers don't plan to scale it up, but down. Their goal is to make one the size of a fingernail with a camera attached. Soldiers would be able to use such a device to scout nearby areas without exposing themselves to hostile fire.
At the link, you can watch a video of the Monocopter in flight. Link -via Geekosystem | Photo: Lockheed Martin
Unless they can actually get them down to the size of a maple seed, the advantages they have over quad-copters are slim and none.
Besides the processing power required for stable flight, the video processing requirements (either airborne or on the ground) are very high, since the camera is spinning at the same rate as the bird.
Interesting concept, but doubtful it will win out over the quad's.