The main principle of this kickstarter is the well known differential GPS. http://en.wikipedia.org/wiki/Differential_GPS.
On the other hand they seem to have some sort of inertial dead reckoning at play, otherwise the claimed 50Hz updatedate would be hard to achieve. I think the Kickstarter is a little bit nebulous on that required 2 GPS setup on purpose. You will not be able to fly with cm GPS precision without having a Groundstation of some sort.
A true hobbyist could do this with 2 ublox gps and 2 dataradios and some computer on the ground (raspberry pi etc) probably for 100$.