In this article we study Figalli and Gigli’s formulation of optimal transport between non-negative Radon measures in the setting of metric pairs. We carry over classical characterisations of optimal plans to this setting and prove that the resulting spaces of measures, \(\mathcal {M}_p(X,A)\) , are complete, separable and geodesic whenever the underlying space, X, is so. We also prove that, for \(p>1\) , \(\mathcal {M}_p(X,A)\) preserves the property of being non-branching, and for \(p=2\) it preserves non-negative curvature in the Alexandrov sense. Finally, we prove isometric embeddings of generalised spaces of persistence diagrams \(\mathcal {D}_p(X,A)\) into the corresponding spaces \(\mathcal {M}_p(X,A)\) , generalising a result by Divol and Lacombe. As an application of this framework, we show that several known geometric properties of spaces of persistence diagrams follow from those of \(\mathcal {M}_p(X,A)\) , including the fact that \(\mathcal {D}_2(X,A)\) is an Alexandrov space of non-negative curvature whenever X is a proper non-negatively curved Alexandrov space.