you should just go with the package from bahn brenner! good price and a complete package, and you cant go wrong with a lightened fly wheel. just check the teeth on the starter to see if they are worn. new flywheel usually means new starter on cars with high miles.
even though all the points people have made so far are good ones its not a flawless mod, heres why i belive its not: a) you stall much easier, either in neutral, between gears, etc b) your car will drop a lot of RPMS between each gear with one. they're just harder to drive, not as streetable. If your going to do it consider that stuff, i mean its not a bad mod. But for the money what else could you get that would improve the car and be more streetable if you know what i mean.
I recently replaced the clutch/disc in my jetta III and was also at the same time highly considering replcing my flywheel with an ultra light aluminum flywheel. After talking to several people and considering the good/bad, i decided to simply have my old flywheel resurfaced, always a good idea if you are replacing the clutch. First of all, VW uses sachs flywheels to begin with which are high quality and generally somewhat light as compared to some that other car companies use. Second of all, while a lighter flywheel increases the speed that your engine can rev, which allows you to shift faster, it is also harder to drive on the street since you must let out on the clutch at a higher rpm. Thus, i think unless you are really into alot of racing and not much street driving, I would think that it's better to maybe just have your flywheel resurfaced.