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) Pentamer of two alpha chains, two beta chains and a gamma chain. Belongs to the FrhB family.