How difficult is it to remove conductors from this type connector?

You can simply cut the wire at the edge of the wire connector and strip back a little bit more of the jacket. THey really aren't designed to release the wire or reuse them.

These connectors work well. I always twist the connector clockwise until I get a strong twisted connection. To be sure I tug on each of the wires to make sure all are well connected. If later you need to take away a wire or change it for another one, just twist the connector in the opposite direction to loosen the wires.