I used one for a couple of weeks last summer while backpacking. I used it with a Sony A6000 and pancake lens and found it secure and convenient. It also has a secondary safety latch that is easy enough to use once you get the hang of it. It is easy to stow and release the camera.
However, I wouldn't use it with a heavy camera like an SLR, not so much because of doubts about security but because of the weight imbalance and the fact that it would sag too much. That said and weight aside, I still wouldn't use it with my MP precisely because I would probably worry about some kind of catastrophic failure, warranted or not. But then again, I don't have much desire to take a heavy rangefinder and lenses backpacking.