Either way I have no input with anything heavier than the 80-200 on a pro body. Regarding gear safety, the FastenR-2 is not at risk of coming unscrewed so long as the rubber washer is compressed and you're using the ConnectR-2. The prior FastenR lacked a good compression washer and the prior ConnecrR had multiple points of failure and is a liability for anyone still using it, IMHO. Unscrewing is not a failure mode you should worry about.
I agree, if I had even the slightest concern that the new design solid 1 piece connector might fail, and drop $20,000 worth of cameras and lenses on the floor, I can guarantee you I wouldn't use it. I have no such concerns, and regularly us this system. If you are realy concerned, there is a way that you can employ a second line of defence in case of connector failure, I also have the two ends of the OP-TECH strap system connected to the cameras regular strap lugs. If you clip these together through the Black Rapid strap, I found (before the BR system proved itself to me) that they in no way impeeded the cameras sliding upside down on the BR straps, but would catch the cameras if the screw connector failed.