In his Featured-in-Physics PRL Letter, Feigel uses relativistic Lagrange formalism to analyze momentum transfer between matter and EM field in a moving dielectric medium, which is isotropic, nondispersive, and uniform, observed in the medium-rest frame. In Feigel's formalism, Minkowski approximate constitutive relation is taken into account in invariant Lagrangian density formula_8. However, Lagrange formalism "gives no new clue on the interpretation of the "macroscopic" Maxwell equations", as criticized by Tiggelen and Rikken, because the validity of Lagrange formalism is identified with whether the Euler-Lagrange equations generated by the Lagrangian density formula_9 under the principle of least action are the same as Maxwell equations. That is to say, it is the Maxwell equations that are the "first principles" for descriptions of macroscopic EM phenomena, instead of Lagrange formalism. From this, Lagrange formalism is supposed to be equivalent to Maxwell equations; otherwise, Maxwell EM theory would not be complete. Thus in principle, the criticism by Tiggelen and Rikken makes sense, and the difficulty how to correctly define the momentum of light in the Maxwell-equation frame would not be disappearing in Lagrange formalism.