i had a atk5k before i bought my go pro 1080 (through pinkibike)
it was a brilliant choice
old tube style cameras are not mountable as chest cams (easily or neatly)
the at5k stuck up high on my lid causing the helmet to feel top heavy, mounted on the side it tilted the lid unless i did it up super tight wich then gave me head aches.
the angles changed as the helmet moved about.
the footage always looked ‘flat’ as it’s from the head, chest is best!
i’ve not used any of the other go pro mounts so my advice would be to get either the 960 (if you’re not bothered by the additional 1080 features) and a chest mount.
Absolutely brilliant bit of kit, made better with the new software (1080) allowing 1 touch recording.
remember CHEST IS BEST 😉