Whats the down side to buying a £11 VAG-COM cable from eBay?
You can only read DTC errors and perform a reset.
I believe it gives you the DTC error numbers and does not give the actual "text" meaning.
You are limited to using "old" software versions of VAG-COM and can not utilise the latest version 805, hence newer cars may not be supported.
No ability to access the "Advanced" features of VAG-COM, i.e. programming & configuring modules (required if repalcing a module), monitoring measuring blocks, etc.
Non-Genuine cables are very unreliable with regard to communication - may not always work! This is because they rely on software drivers on your PC to emulate a genuine cable. However, Gen Cables have a software/hardware installed in the actual cable to correctly communicate with the car.
Non-genuine cables have a tendancy to "blow up" the cable driver circuit and then become "dead" if you have a after-market stereo which may put +12v on the diagnostic pins. Genuine cables are elctrically protected to overcome this.