This document compares grid design and modeling capabilities between Delft3D-FLOW and the new flexible mesh module D-Flow FM. It finds that D-Flow FM requires fewer curvilinear cells than Delft3D-FLOW for the same accuracy due to its improved friction formulation. Case studies of the Wadden Sea and Venice Lagoon show that D-Flow FM runs over twice as fast as Delft3D-FLOW on the same grid and provides comparable accuracy, though higher resolution grids in D-Flow FM increase runtime significantly. The document concludes that D-Flow FM has accuracy advantages but care must be taken in grid design and numerical settings to optimize model efficiency.