Switching off with the key will probably kill power to the logger, which might screw up their data collection. You'd need to install a kill switch to get around that. Or, just don't kill the engine for the 30 days it's in the car.

If the main thing they're actually watching for is hard braking, that's about the LAST thing an efficient driver does. I really wouldn't be worried about any techniques that would "red flag" an efficient driver.