The subject of the user evaluation discussed in this paper is a tool that was developed to support the comprehension of large industrial component-based software systems in the maritime domain. We discuss the context and motivation of our research, and present the user-specific details of our tool, called FlowTracker. We include a walk-through of the system and an overview of the profiles of our prospective users. Next, we discuss the design of an initial qualitative evaluation that we have conducted. We conclude with a summary of lessons learned and challenges that we see for user evaluation of such domain-specific program comprehension tools. Keywords: user evaluation, domain specific tooling, program comprehension, software visualization.