Recently, the potential of metamaterials and phononic crystals to cope with conflicting requirements for obtaining lightweight structures with desirable noise and vibration properties has been demonstrated. These, often periodic, structures are commonly studied based on their representative unit cell (UC) of which the vibro-acoustic performance is examined by means of their wave propagation, visualized by dispersion curves. Typically, the UC is discretized using a finite element technique to capture the possibly complex geometry. This leads to a high computation cost for the dispersion curve calculation which can be strongly reduced by applying modal-based model order reduction techniques such as the (generalized) Bloch mode synthesis (GBMS). In this paper, the choice of the UC is shown to have an impact on the dispersion curve calculation time. Moreover, the efficiency of GBMS strongly depends on the UC choice. The highest reduction in computation time is accomplished when the number of boundary degrees-of-freedom is limited.