few issues with it:
you need 2 serial ports...seeing as you will more than likely be using a laptop, they only have one serial port and adding one isnt possible unless u use like a usb to serial but then they use virtual ports so may not work. and youre unlikely to take your desktop machine outside with you...
also fault codes can be read via stomp test and the service reset can be done with a lengh of wire.
I cant see what use it is to most of you, that will be just wanting to read fault codes and reset oil lights.