I got this GPS yesterday after buying various others from that site that said they had a compass but didn't.
You plug the 4 wire lead into the main port and the 2 wire into the flexiport.
As stated you will need the latest branch of GCS or wait for the next release.
You will be pleased to hear that that it works and i successfully got my quad to fly with position hold and GPS assist.
tip - you will need to set the mag orientation to roll - 0 pitch - 180 yaw - 0, this is because the mag is mounted upside down.