I've used that brand of connectors & I think they're the berries (as they say in the Mountain State). This picture shows the only problem I've found with them. If the edge of the KO is distorted when removing the KO, then the connector may not seat properly and could pop out immediately or at some later time. Once the installer is aware of this, he'll usually give the connector a tug to make sure it is properly seated.
Few things are harder to put up with than the annoyance of a good example.