Althou I love the GoPro I also find it one of the biggest frustrations when shooting with it on the DJI Phantom 2 due to its fish eye lens effect. So I bit the bullet and purchased another GoPro Hero 3 Black with a after market 5.4mm lens attached from Peau Productions.
This effectively gives you a 35mm lens equivalent of 29.97mm lens or a horizontal field of view reduced from the native GoPro’s 123 degrees to a narrow 66 degrees. This effectively gives you a flat or distortion free image (useful for real estate videos/stills or anything else with straight vertical lines).
Am busy testing at the moment and hope to have a video review up with some examples very soon…so stay tuned.