The effectiveness of self-monitoring in anticoagulation therapy often depends on the quality of mobile applications used by patients. This paper presents a comparison of four such apps to determine how their design impacts practical usability. The analysis combined an eye-tracking study with 15 users to evaluate interface intuitiveness, technical performance tests (CPU/RAM usage), and an analysis of notification systems. The results reveal major differences in usability, where clear interfaces led to better user performance. The study concludes that an application's design is a critical factor that can directly support or worsen the effectiveness of patient therapy.