The Pro-Kit is intended for independent repair shops, particularly ones who need to work on all different years and models of VW/Audi and who may not have internet access at the shop. It comes with stuff you probably don't need, like VAG-COM on CD (just download it), an adapter for older cars (no US TDI needs this) an extension cord and so on.
Assuming you're an invividual TDI owner and your PC has a serial port, you should choose either UNI-COM ($199) or, if you want some additional convenience and speed, a HEX-COM ($279).
-Uwe-
