I have come across this thing in a few of the MSnS pages but am not usre what it is and if I need one?

It is a valve which is controlled by the ecu, separate from the throttle body, which has its own air intake. Its function is to maintain a steady tickover and mainly works when cold.

It's a valve that bleeds a bit of extra air past the throttle butterflies when the engine is cold to increase idle speed.

The latest MS units with the right software will control a PWM valve (gives variable flow) and will keep the engine at a specified RPM regardless of external effects. This is generally unnecessary and is provided more so that people can interface the MS with their existing EFI systems. For the rest of us a simple fast idle solenoid is fine, or even just keeping your foot on the throttle for the first coupleof minutes will suffice for most!