Age-friendly smartphone launchers are tools designed to enhance smartphone handling among older adults with cognitive and functional limitations. Although evidence exists about the positive effects of age-friendly smartphone launchers on older adults’ usability performance in general, little is known about how the design and interface complexity of these launchers affect their interface usability effectiveness and efficiency compared with standard Android smartphone interfaces. Thus, in this study, a randomized crossover experiment involving 50 older smartphone users, aged 60 years and above, was guided by the principles of summative usability testing to assess whether an age-friendly launcher performs better than a standard Android launcher performs and to investigate the relationship between the user interface complexity and usability performance of launchers. The results of usability tests in which each participant solved 10 tasks on both launchers indicate that the two tested launchers had comparable effectiveness (i.e. completeness with which participants achieved the test tasks’ goals), whereas the age-friendly launcher marginally outperformed its standard Android counterpart in terms of efficiency (i.e. the amount of time used by participants to solve the test tasks). The results also demonstrate that lower user interface complexity is associated with higher effectiveness and efficiency, suggesting that age-friendly smartphone launchers might lead to higher adoption rates of smartphones among older adults if interface designers could reduce their cognitive complexity by limiting the number of steps and alternative paths for task completion.