Experienced modelers go to great pains to tie down their servo and throttle leads, and some find unplugging a Castle controller from the RX disrupts all their work. Many have asked for something like a Y connector that gives an open lead for easy Castle linking, but a traditional Y harness doesn't work when the other branch of the Y is connected to an RX, the signal line must be disconnected from the RX.
Castle Quick Connect does just that. It detects the presence of a Castle Link adapter on the free lead and switches the controller's signal line from the RX to the Castle Link. Easy as that.
Follow the Connection Diagram (found on the inside of the package) when connecting the Quick Connect. Don't forget to use the included piece of heat shrink tube to secure the ESC lead to the Quick Connect.