The regulations require approved restraint for take-off and landing. Your rig might not qualify for that, and you intend to use the aircraft-installed seat belt for TO/Landing. The regs do not require any restraint when in flight. Therefore whatever you chose to wear when in flight and legally "unrestrained" - even something that is linked to an existing hard-point - is "free choice".
I think Wrench1 gave the relevant regulations. He also gave the very relevant "check your insurer".