I used to make third party scan tools. My advice is don't drive a BMW farther from a dealer than you will pay a tow back. Not that they are unreliable cars, but that our tools were far better than our competitors at BMW and I wouldn't give them a passing grade. (BMW writes their own tools). Of course I left that job in 15 years ago, maybe things have changed.

For other makes of cars third party scan tools work pretty well at diagnostics.