P2V and Ziggi-HD essentially serve a similar purpose but different needs.
The P2V is more of a portable device as its name suggests: Point to View, where you could use it in a variety of ways and detach the camera head to shoot in more angles as you seem fit. This would be great for Art and Science classes where you may have to be projecting objects that are not a flat surface. There are also more accessories for P2V which prepares P2V for different type of tasks.
The Ziggi-HD, our latest addition is geared more towards a stationary type of presentation needs. We've made some design modifications so the stand on the Ziggi is taller, thus capturing A4 size documents more easily than using a P2V. The improved HD camera lens gives Ziggi-HD a decisive advantage over P2V resolution wise. Plus the new 6x zoom, Ziggi-HD is perfect for capturing fine detail on a larger document/material. The Ziggi-HD also comes with an anti-glare shield, which attaches to the camera and reduce the light reflection directly over, say a tablet device, which could create a glare on the screen.
Both models are small and portable USB powered document cameras, and it is really how the teachers use the cameras that would determine which model is a better fit.
For a spec overview, please refer to the comparison chart on the product page, or download the comparison chart in pdf format.