The big thing with longevity is maintenance. I've seen chains last thousands of miles and some last 500 or fewer. Nothing broken, just totatally worn out. The short lived ones are always on people bikes where they literally haven't lubed their chain since getting it, and 12 speed chains show their wear worse. Not that they're not as strong, especially in the directions they are stressed the most, but the tighter tolerances between chains and cogs lead to degraded shift performance faster if the chains aren't maintained, sram and Shimano included. It's also why I would never run a kmc...