A servo driver is a simple device generally used to test servos. Plug in power on one end, the servo on the other, and use the potentiometer to control the position of the servo. The 555 timer creates the correct pulses to drive the servo.
The purpose of this switch is to take in the servo pulse from a RC receiver and turn that into a digital output. These kinds of switches are used commonly on battlebots to trigger weapons. The current version can be constructed for either high-low or low-high output configurations.
Servo pulses can easily be corrupted by EMF from motors and other noisy devices. What the noise trap does is clean the pulse into a nice square wave. This comes especially handy when the pulse generator (microcontroller, RC receiver) is located far away from the servo, as the wires will pick up a lot of noise. Placing the noise trap close to the servo will result in a cleaner square wave going to the servo.