I've had several swivel ball links fail. The usual failure mode is the thin plastic around the ball breaks. I even had one come off the ball. Haven't lost an airplane to them yet, and I still used them for everything. You just have to make sure you have a washer or large locknut over the ball so the plastic gets caught if it cracks and slips off. These were on links with the 2-56 bolt thru the ball with either 2-56 or 4-40 pushrod ends. I've seen some manufacturers advertise they have extra thick plastic around the ball on their product. Makes you wonder why they would do that????

If you fly them enough you will find they do wear. Either the ball will get real loose in the plastic and snap out easily or, if you don't thighten down the bolt real good, the threads on the bolt will eat out the inside of the brass ball. This happened on my Sukhoi to the point where I had to replace them.

Like anything else you have to do a feel good check on them once in awhile.