Update:
I received the OBD2 reader today. I have the free version of Torque. I just tried it out to see if it would read, it worked on both my vehicles. I will play with the paid version tomorrow and use it on a trip to work. I'm a little nervous about having the reader in while car is in use. Are my fears unfounded? I have no stored faults.

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'03 Black BMW E53 3.0i 110,000+ miles
'03 Black Mercedes-Benz W211 125,000+ miles
'13 White Mercedes-Benz W2o4 New