Too early to say, only had it for nearly 3 days. But the mild hybrid seems to function exactly as advertised, when I engage the eco button located below the shifter, it's on. When I stop at a stop light or traffic, and put it in neutral, and foot on the brake, the engine stops instantly. When I put my foot on the clutch again, it starts right away. GM and some other reports I have read says it can add 5-10 percent on the already great fuel economy of the diesel engine. Kudos to GM for finally coming out with it. As many have said, I wish too they would come out with it in North America, it seems to be a great engine in a nice car.