Driver assistance systems aim to make driving safer and more comfortable while increasingly used in all vehicle classes and almost all markets. However, current research results continue to show low customer satisfaction and user acceptance. This is mainly due to the fact that the user experience and the holistic consideration of driver assistance functions as well as the human-machine interface (HMI) were neglected during development. A consequence of this is a low level of utilization, resulting in unused safety potential. In this paper, we present a comprehensive evaluation method for driver assistance systems in terms of the combination of HMI and functional performance, especially for the Lane Keeping Assist (LKA) and Adaptive Cruise Control (ACC) systems. For this purpose, a test person study was conducted in close cooperation with Volkswagen Brazil and MdynamiX. The aim of this approach is to identify weak points of driver assistance functions in combination with display and operation (HMI). Based on these findings, concrete measures are derived to increase customer satisfaction, to increase acceptance during use and thus also to increase the degree of use. In the context of this test person study, the complete user experience (before, during, after the journey) of drivers during a real journey with two different vehicles was surveyed by means of questionnaires. In addition, the functional performance of LKA and ACC was recorded by means of objective data collection. Thus, this work represents a holistic methodology for user-centered development. The work highlights the need for advanced development of function, operation, display and warnings with a strong focus on the needs of customers to enable clear communication regarding system state and boundaries. In this way, functions can be developed that increase both the level of use and safety, as well as driving comfort. First and second tier suppliers, but also service providers for "user experience", "usability" and "human-centered development", benefit from this work. The findings are crucial for optimizing driver assistance systems and better meeting customer expectations. The study is characterized by the holistic view of HMI and function from the customer's perspective. Through this approach, targeted improvements can be made to meet customer requirements and expectations.