Buy BMW K+DCAN Scanner or ADS interface

If your car has a metal contact fitted and voltage on pin 15 of the round 20 pin diagnostic port, there is no way the interface you are looking at (i.e. BMW K+DCAN 2.20) will provide diagnostic access to all modules.
Secondly, unless you are planning on buying another car built after 03/2007, the DCAN feature is a wasted feature. I have several ADS interfaces (all of which require a true serial port connection), Modded VAGCOM interface, K+DCAN interface and a couple of others.
For working on OBD compliant cars (i.e. cars built prior to 03/2007) I rate the K+DCAN interface at the rock bottom of the heap. Why? Because lots of them require modification to read pre-2007 K cars (i.e. pins 7 & 8 need to be joined) and if you do this mod, they need to be un-modded to use with post 2007 DCAN cars. You also need to configure the interface using DCAN.exe before you use it.