Dinan answers the warranty question here
. Some key passages include:
"The installation of Dinan Performance Products and systems may affect the vehicle manufacturer's new car limited warranty. The vehicle manufacturer's new car limited warranty may not apply to modifications to a vehicle or the installation of any performance accessories or components attached to the vehicle which substantially alter the original engineering and/or operating specifications or which result in damage to other original vehicle manufacturer's components."
In other words BMW 'may not' (for practical intents and purposes 'will not') warrant Dinan products. This looks to me like it's the same warranty policy as any reputable tuning company. Our local dealerships, in conjunction with the BMW corporate regional reps, would treat a fault that they considered caused by Dinan the same way they would one caused by a Helix part: they would deny the warranty fix.