The availability of high quality, free-standing GaN substrates enables new device applications in III-nitrides, especially for vertical device structures. With the introduction of these native substrates, the properties of nitrides are no longer dominated by defects introduced by heteroepitaxial growth. However, additional materials challenges are coming to the forefront that need to be understood and surmounted in order to allow homoepitaxial devices to achieve their full potential. In this paper, 2 mu m of UID GaN are grown simultaneously by MOCVD on three commercially sourced 2 '' HVPE wafers. By doing so, the substrates are exposed to the exact same growth conditions and the influence of the substrate can be unambiguously identified. The results are presented in regards to the effects of the substrates on epitaxial film morphology, uniformity, impurity incorporation, substrate/epitaxy interface, and electrical properties.