This paper presents insights from a research study, which involved the use of a Rapid Modular Prototype (RMP) to augment user interviews. RMPs are a combination of interchangeable modules made from tangible materials and physical computing components, such as Arduinos and Raspberry Pi. In our research study, we created a prototype to inform the design of parking meter interfaces. The modular approach to designing the prototype, which led us to the concept of RMPs, was driven by the need to carefully assess and compare various input mechanisms, such as knobs versus buttons, and their efficacy, for example, for selecting the time period on a parking meter. Reflecting on our experiences developing the prototype and its role in supporting our participant interviews, we examine how RMPs can be used as a tool in interviews to gain rich insights from research participants.