The improved accuracy of DM21@B3LYP over B3LYP@B3LYP demonstrates the significant potential of machine-learned density functionals in transition metal chemistry. Despite its potential, energy refinement on B3LYP densities with DM21 is currently not costeffective, as a single SCF iteration of DM21 in PySCF for medium-sized molecules can exceed by far the total time required for a B3LYP or even B2PLYP calculation. Carrying out DM21 with B3LYP orbitals seems to offer a useful compromise once DM21 is coupled with a more efficient implementation of the exact exchange energy density .