This is a question we have been asked a few times now and here is the difference:
The Gruppe M system is the same type of intake design as found in most aftermarket intakes. By that I mean they use a cone filter mated to the MAF tube and the carbon fibre is just a heat shield surrounding the cone. In this configuration - the airflow has to negotiate a path from the large diameter at the base of the filter through to the smaller diameter of the MAF tube in a relatively short distance. This is not great for aerodynamic efficiency as you will get dead spots and some turbulent effects.
The Eventuri is a new type of intake design which is patent pending and this is why: We use a cone filter - BUT here it is inverted and decoupled from the MAF tube. The filter is now mated to the front of the carbon housing and by inverting it we are capturing maximum surface area for incoming airflow. Now, the carbon housing is not merely a heat shield - it shapes the flow smoothly down to the MAF tube over the entire distance of the housing. This means that we keep laminar conditions through the path into the MAF tube which is a lot more efficient. On the road - this translates not only to more power but smoother delivery and a sharper throttle response.
That's the main difference between the Eventuri and other systems. Plus for the Z4 kit - we have also used an additional heat shield to stop hot air from the radiator from entering the intake as well as a cold air scoop to direct cold air directly into the filter which actually keeps IAT's lower than the sealed stock airbox.
Hope that helps clarify things.