I have one and it is a great addition.
It plugs into the data port in your left kick panel on the driver's side of the car. The port is dangling next to your fuse block.
I got it because my HUD was down and used it for a speedometer.
It can be taken out and used on other cars in 5 mins.
I have even used it on my friend Frank's car and he has a S14 with a SR20DET from a S14. We did his wiring right out of the S14 manual so it looks like everything went well.
Good luck with the group buy fellas. I know I had to wait an extra 6 months because a group of 300zx guys got a group buy going and bought all of the dealers stock.
There is also an audible warning sensor you can connect to the MDM100N. It has a light and a ringer to warn of you set points you have passed.
There is another cool item. It is a device that displays all of your readings on a video screen. You can run an in car camera and get your speed, RPM etc. Just like the police shows.
I am sorry if the post is rambling but I love my MDM.