Hmmm, I'd be careful with "swivel mount safety tethers"
Ever seen what a seatbelt "Spinning in the breeze" can do you your airframe?
Not suggesting it's a bad idea, just make sure your tether is long enough to easily clear your aeroplane!
A spinning tethered object in the slipstream would do a lot of damage to whatever surface it was pounding against, probably punch a hole in a fabric surface, and possibly the same on a metal skin if the tether was long enough.
Too long a tether runs the risk of being wrapped around the air-frame and/or interfering/jamming a control surface.
Before anyone does it in an aircraft where life and limb are at risk, tether a loose camera to a car, preferably your own, drive at 160kph for 15 minutes and see what damage it does.
