While mixed prototyping has proved to be effective for the assessment of prototypes, this research aims to explore the use of mixed prototyping for the generation of early prototypes. To satisfy end-user’s needs, new products need to be designed with an early integration of end-user requirements. An efficient way to achieve this is to directly integrate the end-users in the design process and give them an intelligible and interactive tool to perform specific design tasks. Current interactive tools to integrate end-users in the design process provide either a high level of immersion (e.g. CAVE) or a high level of control over the virtual prototype (e.g. configurators). We designed a new mixed reality design tool which simultaneously allows end-users to be immersed in a virtual environment (immersion) and to interact with a virtual prototype and to modify it (control), resulting in effective end user-interactions. In two design use-case scenarios, we assessed the end-user experience and satisfaction while using the tool and we also evaluated the impact of the tool on the creative process and the design outcomes. The findings show that, when users are provided with a tool that allows to directly perform design tasks and modify a virtual prototype, as compared to when they have no control, they are more engaged in the design tasks, more satisfied with the design process and they produce more creative outcomes.