There is no JB4 for the F30 yet. Only the N55 Stage1 tune. It does not leave codes behind but if you are worried they sell a complain tool called the "CAN Tool" that will delete hidden codes. Alternatively you can get the BT Tool which lets you read codes via laptop from all modules on the vehicle.
Gains are 40-50hp and well worth the 5 minute install time.
BEST PRICES GUARANTEED - New N54 Downpipe Intro Special - $319.00
JB4 **G5** On Sale - FREE Shipping Click Me - NEW JB4(N55) & DCI's $95.00
NEW F30 N20/N55 ER Downpipes and Chargepipes - BMS OCC (On Sale)