One of the most common limitations of software is poor usability. Usability refers to the effectiveness, efficiency, and satisfaction with which users achieve their particular goals in a particular context. This paper reports an experiment which evaluates the usability factors between two software process modeling systems, EPF-Composer and DSL4SPM. Based on the standard ISO/IEC 9241, a method has been designed for both subjective and objective evaluation of systems' usability. The method allows gathering the metrics that make up the usability scale. Our experiment, involving 14 teams, provides insights on how to enhance the design of software products. The results shows that a combination of objective and subjective evaluations provide a more complete view of usability.