The 3BaysGSA Pro plugs into the back of your grip, where it collects data on your swing, and relays that data to software on your phone. The internal 3d accelerometers and gyroscope sensors are said to be able to track up to 10,000 points on your swing.
Once the data is on your phone, you can see an animation, showing either side of back views. This should offer some pretty good feedback on the state of things.
In addition to the animation, the software will show you club head speed, face angle, swing path, tempo, down swing time, back swing time, impact force, ball speed, carry distance and consistency. The data can then be stored by club to see your progress. Finally, golfers can compare their swings to reference swings from professionals.
There are versions for both Android and iphone.