Reduces the physiological low-potential two-electron acceptor coenzyme F420, and the artificial one-electron acceptor methylviologen. H(+) + H2 + oxidized coenzyme F420-(gamma-L-Glu)(n) = reduced coenzyme F420-(gamma-L-Glu)(n) There are 12-13 Fe atoms per alpha/beta/gamma unit of the FRH. Heterocomplex of the form (alpha(1)beta(1)gamma(1))(8). Belongs to the FrhB family.