I'm a great fan of KMC chain connectors and use the 10C version with my Campag chains. Checking my chain for wear, I've found that that it is standing up very well to my recent mileage increase but, by using my Prolink chain wear tool across the a length of chain including a connector, the connector appears to be wearing i.e. stretching more quickly than the rest of the chain. Therefore, although these links are reuseable from a dismantle-and-clean-the-chain perspective, I recommend keeping an eye on them, if your use them, and replace them as necessary and not to just wait for the chain itself to need replacing.
Portsmouth North End Cycling Club Forum