  We argue that claims about magnetic field dependence of the magnetic field
penetration depth lambda, which were made on the basis of moun-spin-rotation
studies of some superconductors, originate from insufficient accuracy of
theoretical models employed for the data analysis. We also reanalyze some of
already published experimental data and demonstrate that numerical calculations
of Brandt [E.H. Brandt, Phys. Rev. B 68, 54506 (2003)] may serve as a reliable
and powerful tool for the analysis of the data collected in experiments with
conventional superconductors. Furthermore, one can use this approach in order
to distinguish between conventional and unconventional superconductors. It is
unfortunate that these calculations have practically never been employed for
such analyses.
