Hi Dave
The reason for the quick release plate is to allow you to fit and remove camera equipment quickly and securely without the aid of any tools.
It was designed to allow the mounting of any equipment, have a look at the mounting holes on the removable plate.
Top mount is for stills or video, due to the shape of a lot of the newer sony cameras it is safer to top mount the video camera, in answer to your next question of where do you mount the stills camera ??? i would look at using an FF2 Kryten and mount the camera on the front mount or making a stills mount for your stills camera.
I used to use a flat top pro which is a heavy and expensive helmet, it does the job well but not everyone jumps that much to justify it. Basically you don sell many of them which means the retail cost is quite expensive.
Any side mounted camera is subject to line snag unless it is fully enclosed, i.e. FF2, FF3, FFX
I have mounted a lot of these mounts now and they are also used outside skydiving.
I hope this helps and it is better than some of the things you see leaving the plane on people heads !!!
Regards
Gary