I've got several different varieties of quick release harnesses and none of them work reliably over time. I do maintain them (cleaning, greasing, etc.). I've got one like the one you picture that has some detent keeper balls and I think that's probably the best type...although, on mine, the detents are too deep and it too has a hard time unlocking if it's loaded up. I've used the pin type with a retainer clip and they're terrible for corroding and even in good shape, if you try to release the hook with a side load on it, they don't like to come out.

A good safety knife is a good idea too. I like the kinds with the replaceable razor blades like this (as long as you can find a good sheath):

http://www.meltontackle.com/products/zak-s-safety-knife.html