When swift, accurate appraisal of evidence is required to inform policy concerning broad research questions, and budgetary constraints limit the employment of large research teams, researchers face a significant challenge which is sometimes met by reviewing existing systematic reviews. In this paper we highlight the challenges inherent in the reviews of reviews (RoR) method in order to advance understanding of this important tool for policy makers. Drawing on our experiences, we present, where possible, potential solutions to these challenges to demonstrate that RoRs, despite their limitations, can be useful for mediating policy-relevant evidence at speed.