Background: A scientific consensus on the public health impact of electronic nicotine delivery systems (ENDS) remains elusive. This is partly due to the wide variation in product characteristics often lumped together under one category. Research is needed to better understand what ENDS device type characteristics motivate their use by adults. Methods: Nine focus groups of 32 current ENDS users who were 18+ years old, had used ENDS in the previous 30 days, and had been using ENDS for more than two months were held either in person or online between February and June 2020. Results: Participants’ reasons for their choice of ENDS characteristics included both general, applying to all ENDS products, and specific, relating to particular ENDS devices. Health benefits and the lack of offensive odor were commonly identified as important reasons for using ENDS in general. Flavor and product discreteness were both general and device-specific determinants of ENDS use. Conversely, nicotine delivery, cloud size, battery properties, aesthetics, ease of use, and cost were device-specific drivers of participants’ choice. Conclusions: The reasons that adults choose to use ENDS are complex and sometimes related to both ENDS as a category and as specific ENDS product types. Regulations and public communication campaigns should reflect their ultimate objective and consider both general and specific motivations when attempting to achieve public health objectives.