As far as master links go, the KMC Missing Link is on the top of our list. The Missing Link's function is simple, consisting of two symmetrically opposing links that disconnect and reconnect with minimal effort. Once the links are engaged, however, their connection is quite secure.
The Missing Link is an excellent option for bikes that require frequent drivetrain cleanings. Also, when paired with a small chain tool in your saddle bag, it can be invaluable in the event of a broken chain.
The ten speed Missing Link is officially compatible with all ten speed KMC and Shimano chains, but we find that it works well on all models of 5.88 mm wide ten speed chains.The nine speed Missing Link is compatible with all nine speed chains of 6.6 mm width.