Objective To explore optimum use of the Odon Device by establishing the optimal device design, describing the ‘usual’ steps for use and setting clinical parameters for device use. Design Qualitative case study methodology was embedded in the ASSIST Study – a feasibility study of the Odon Device. Setting Central Delivery Suite, North Bristol NHS Trust, UK. Population Women who required a clinically indicated assisted vaginal birth. Methods Each case was determined by the single use of the Odon Device and could contain data from one or more of the following: formal observation of the Odon assisted birth, an interview with obstetricians, midwives or women involved in an Odon assisted birth. Data collection and analysis ran iteratively and in parallel enabling rapid dissemination of findings. Main outcome measures Determining the optimal steps for device use, recommendations for optimal device design and defining clinical parameters for device use. Results Optimal steps included applying the device during rather than between contractions, having a flexible approach to the application angle and deflating the air cuff sooner than originally proposed. Three design modifications were proposed. The device can be used under local or regional anaesthetic and is successful with all vertex presentations. It is not successful at assisting birth when the vertex is at station spines. Conclusions Case study methodology facilitated rapid insight into optimum device design, device use and key clinical parameter for successful use. This methodology should be considered whenever innovative devices are introduced to clinical trials and settings.