Mobile device usage in online surveys has steadily increased in recent years. As mobile devices differ, for example, in their handling, from computers, device effects within online surveys are found for several data quality indicators. However, results concerning these device effects are neither comprehensive nor conclusive because existing research are often based on non-optimized designs or do not account for the type of mobile device, for example, smartphone or tablet. This study uses data from the emigrant sample of the German Emigration and Remigration Panel Study (GERPS) a probability-based online survey (n = 4,888)—which made use of a mobile-optimized design—to compare data quality between smartphone, tablet, and computer respondents. Propensity score weighting was employed to account for device choice selectivity effects. The data quality indicators showed mixed results and smaller data quality differences across computers, smartphones, and tablets compared to previous studies. Higher dropout rates on mobile devices and here especially on smartphones remain the major challenge for survey participation, especially on small screens. However, our results render mixed-device data collection via mobile-optimized online surveys as a promising data collection approach, especially for exploiting the large response potentially associated with smartphone and tablet respondents.