Background E-cigarette advertising, which often includes various features, may prompt e-cigarette use and product switching. This study examined the associations between noticing e-cigarette ad features and perceived product appeal and interest in completely switching from cigarettes to advertised e-cigarettes among young adult dual users of both products. Methods We analyzed data from an online heatmap experiment among young adult dual users defined as established cigarette smokers who currently used e-cigarettes (ages 18-34 years; n = 1,821). Participants viewed 12 e-cigarette ads, clicked on ad features (e.g., fruit flavors, nicotine warnings, price promotions, smoker-targeted claims) that attracted their attention (defined as “noticing”), and answered questions about e-cigarette product appeal and interest in completely switching from cigarettes to the e-cigarettes shown. We examined within-person associations between noticing specific ad features and outcomes, controlling for demographic and tobacco use-related characteristics. Results Noticing fruit flavors (AOR = 1.67 and 1.28) and fruit images (AOR = 1.53 and 1.21) was positively associated with having any e-cigarette product appeal and switching interest. Noticing price promotions (AOR = 1.23) was positively associated with product appeal. In contrast, noticing nicotine warnings (AOR = 0.74 and 0.86), smoker-targeted claims (AOR = 0.78 and 0.89), and tobacco flavors (AOR = 0.92 and 0.90) was negatively associated with product appeal and switching interest. Conclusions Noticing certain e-cigarette ad features (e.g., fruit flavors and nicotine warnings) may be associated with product appeal and/or switching interest among young adult dual users. More research is needed to assess the influence of e-cigarette ad features that promote product switching interests among cigarette smokers while discourage interests among tobacco-naïve individuals.