  We consider stability of periodic travelling waves in the generalized reduced
Ostrovsky equation with respect to co-periodic perturbations. Compared to the
recent literature, we give a simple argument that proves spectral stability of
all smooth periodic travelling waves independently on the nonlinearity power.
The argument is based on the energy convexity and does not use coordinate
transformations of the reduced Ostrovsky equations to the semi-linear equations
of the Klein--Gordon type.
