The tensile mechanical properties and anisotropy levels of identical test-coupons, fabricated from maraging steel 300 (MS300) using two alternative EOS EOSINT M280 Additive Manufacturing (AM) systems, have been examined. The mechanical performance variations resulting from process differences between the two suppliers and the part's build volume orientation (0 degrees, 45 degrees, and 90 degrees) are investigated. Significant microstructural discrepancies, affecting mechanical performance, plasticity and anisotropy levels, have been observed in the as-built samples obtained from the two suppliers. A difference in the angle of the laser scan strategy, in conjunction with unfavourable powder feedstock characteristics, are understood to have had a profound influence on the plasticity and anisotropy divergences observed in the AM MS300 alloy. Plastic anisotropy levels can be largely reduced through application of aging heat-treatments, however, a degree of transverse strain anisotropy is likely to remain due to the AM alloy's fabrication history. Moreover, in this work both the anisotropic and elasticity tensors for this material are derived. These tensors can be used by researchers working on modelling and simulation of the MS300 mechanical properties.