Setting up a gopro or contour can be done in literally 15 seconds, thats from approaching a random car to walking away. Suction cap it to any exterior surface or any interior window, adjust the camera angle and press power/record. Try doing that with a RadCam, its a 15min job that involves cable ties, race tape, etc and is 'generally' limited to interior footage only.
Thier is no off-the-shelf camera on the market today that will give you good sound when mounted externally however just about all cameras will give great quality video for the club-trackday user. Battery comes down to management, if you are sitting in the pits with the camera on for 15mins before you go out on track well yes you will probably run out of battery before a trackday is finished but they all come with chargers and a second battery is quite cheap to carry with you.
Also what are the weight limits for cameras and motorsport?