You need the computer, a speed sensor and a thermocouple for temp. They have a bunch of different sensors available and so you need to figure out what works with your particular bike. I put mine on the Extreme Urban Express.
Due to the high bars, longish forks/frame, and the way I wanted to conceal the wire routing through the frame, I had to buy an available extension wire for the TCouple. You have to make a brkt for the speed sensor and mount a magnet in/on the wheel. They have kits with a variety of assorted magnetic bolt or glue-ons available. I used the front whheel for mine. The tach is just a wire wrapped like 6-8 turns around the plug wire, very simple. TCouple goes under the plug. I also bought the easy mounting bkt and had it mounted to my crossbar in less than 5 minutes.
You can buy a kit for another bike or quad, but you may not get all the parts that work best for your application. I bought my components separate (a bit cheaper) and the first speed sensor didn't work for me so I returned it for another for only shipping. They were pretty cool in working with you with good customer support.
This is a deluxe upgrade for any bike and gives you real-time mearsurements that are invaluable for 2-stroke performance engine tuning (pipes, ports, carbs, HC head, etc.), jetting and driveline variator/clutch tuning. Anything else is just a guess.