Here is the part that is prone to failure. The male QD has a groove that is cut into the housing to secure to the clamp on the female connector. This groove is a stress-riser, and is prone to cracking when under stress.
My QD failed (in my driveway, fortunately) about two months after I purchased one set of metal replacements. Since I had the parts, I was able to make a repair without any incident. Had this happened on the road, and without a replacement QD, I would have needed to resort to a field repair. A Bic pen body and two clamps can get you home in that situation.