The present study propose a performance evaluation index for metal hydride based hydrogen storage reactors. The index relies on an ideal reactor bed design based on homogenous distribution of cooling material. The index is further used to compare the performance of longitudinal fin reactor. The aspect ratio of the longitudinal fin has been varied to investigate in influence on hydriding time. This study has been further extended by considering two new reactor designs one with alternating longitudinal fin elements and the second with two complete longitudinal fins. The later design was found to perform better and showed minimum deviation from the ideal scenario.