Over a period of time the chord that runs in the interior of the jess rots or becomes weaker. I've never had 2 fail at the same time, but I guess it's possible. The ones I've had fail, failed in the same way. Another local falconer has had the same experience.

I really like them though because of the stiffness. I've never had an issue with a bird getting tangled like I have with leather or braided jesses. They are also really quick to change out.