Mashup tools are platforms that enable end users to combine components from multiple sources and thus create, deploy, and share their own web applications. The aim of this paper is to present and discuss the findings of two empirical studies on evaluation of mashup tools by means of subjective and objective measuring instruments. In the first study, data were gathered with the employment of SUS post-use questionnaire and Tobii eye-tracking device, and in the second, by applying the retrospective thinking aloud method. The analysis of collected data uncovered strengths and weaknesses of evaluated mashup tools. In addition, the relevance that users assign to quality in use attributes in the context of mashup tools has been determined.