Inverter-based resources (IBRs) have low inherent inertia, making it difficult to maintain system stability especially with of their increasing penetration. However, Flywheel Energy Storage Systems (FESSs), combined with advanced inverter technologies like Grid-Forming (GFM) and Grid-Following (GFL) inverter sources, offer a promising solution for frequency regulation and stability support. This paper investigates the dynamic performance of a microgrid with integrated FESS operating in both GFM and GFL modes, focusing on their complementary roles in maintaining frequency stability. A coordinated control strategy using MPC is introduced to optimize the response of both GFM and GFL inverters. The results obtained by simulation in Matlab/Simulink and validation on Digsilent/PowerFactory show that the RoCoF increases with the increased IBR penetration. To balance these two IBR interfaces, the focus should be on the GFM-FESS. It should be tuned, which, in this investigation, leads to better frequency response with the same capacity, size, and location. This adaptability makes the FESS a highly effective tool in stabilizing low-inertia power systems and ensuring microgrid frequency regulation.