Mobile health education apps are increasingly used to promote health literacy among adolescents globally. However, little is known about their adoption and effectiveness in resource-limited settings such as urban Uganda. A mixed-methods approach was employed, including quantitative surveys to measure usage rates and qualitative interviews to explore user experiences. Usage rates varied significantly across different age groups (ranging from 35% among 12-year-olds to 60% among 18-year-olds). The mobile health education app showed promising initial performance, particularly in enhancing knowledge about adolescent-specific health topics. Future interventions should focus on targeted marketing strategies and continuous user feedback loops to optimise the app's effectiveness. Mobile Health Education App, Adolescents, Ugandan Urban, Usage Rates, Performance Outcomes Treatment effect was estimated with $\text{logit}(p_i)=\beta_0+\beta^\top X_i$, and uncertainty reported using confidence-interval based inference.