  Saulder et al [2019, A&A, 622, A83; arXiv:1811.11976] have performed a novel
observational test of the local expansion of the Universe for the standard
cosmology as compared to an alternative model with differential cosmic
expansion. Their analysis employs mock galaxy samples from the Millennium
Simulation, a Newtonian $N$-body simulation on a $\Lambda$CDM background. For
the differential expansion case the simulation has been deformed in an attempt
to incorporate features of a particular inhomogeneous cosmology: the timescape
model. It is shown that key geometrical features of the timescape cosmology
have been omitted in this rescaling. Consequently, the differential expansion
model tested by Saulder et al (2019) cannot be considered to approximate the
timescape cosmology.
