Comment on “Collision monochromatization in $e^{+}{e}^{-}$ colliders”

Bogomyagkov and Levichev [Phys. Rev. Accel. Beams 20, 051001 (2017)] have recently reported on monochromatization in collision schemes with crossing angle. From their results, in particular, it may seem that: (1) horizontal dispersion at the IP can provide monochromatization factor $\mathrm{\Lambda }\gg 1$ while retaining Piwinski angle $\varphi >1$, (2) production rate in such a scheme for FCC-ee at 62.5 GeV can be larger than that in the nominal crab waist collision, and (3) strong rf focusing can be used for monochromatization purposes. We demonstrate here that the first two statements are not correct, and the last one is very doubtful.