There is a widely shared view that planning actors require planning support systems (PSS) that can be easily adapted to changing project demands packaged in easy-to-understand formats. Recent studies confirm this and show that PSS are increasingly user-friendly. Still, little is known about under what conditions they add value in practice. This paper tests three hypotheses about PSS performance and usability in an experimental study. 133 students were exposed to different conditions of PSS facilitation flexibility and visualization hardware (tablets versus maptable). They performed identical strategy-making tasks consisting of divergence and convergence. In addition to measuring the quantity and quality of ideas, we assessed perceived process quality and usability of the PSS. Tablet groups performed better on idea generation and evaluated their solution to the planning problem more positively. In contrast, maptable groups performed better on ideational quality and evaluated their experiences in terms of collaboration, more positively. Groups under indicator flexibility performed best in idea generation, while groups under no flexibility received the highest score for ideational quality. Process quality scores were highest under no flexibility followed by indicator only flexibility. Findings suggest tablet use may be more effective for idea generation, an outcome of divergence, while maptables better support group communication, a key aspect of convergence. The study confirms the need for tools and methods that fit both individual and group work. Findings also indicate that identifying structured ways of applying adaptive PSS to the complex world of planning practice may be key to contextualizing such tools.