This paper presents both the pedagogical design principles and the challenges faced during the development of a mobile app, Chinese Characters First Steps, to support recognising, learning and practising writing Chinese characters at beginners' level, including the difficult balance between pedagogy and technical affordances. We also present the results of a research study which collected quantitative data from over 130 users of the app as well as qualitative data from interviews with four users. The results offer a profile of language learning app users and very positive attitudes towards learning with apps. They also reveal users' reasons for learning Chinese, patterns of learning, expectations of the app, and evaluation of the different features for their own personal learning. Finally, the paper concludes that the chosen design principles for the app were appropriate for its purpose.