These mounts are neither acceptable or legal.
Anything attached to a helicopter needs to be approved - these 'home-made' contraptions aren't likely to be approved anywhere.
No approval means the C of A is instantly invalid and therefore the insurance is also invalid.
Simple really.
I do know that there are some operators and pilots who have no regard for these regs and are very happy to fly all sorts of un-approved equipment, but the bottom line is that as soon as they start engines the insurance evaporates.
I wonder how many of these camera guys know this.