Hello, I have looked at the two data sheets from Monacor. The "MF" model is a compact version of the "FGA-40". The distortion factor of the larger model (FGA-40) is slightly better (the slightly different impedance does not seem to be important to me). Conclusion for me: In the car, the small difference in distortion is hardly audible - 0.001% with the big one instead of 0.01 with the small "MF"), but maybe the smaller model is easier to install in the car. However, if you want to use the ground filter with a really high-quality home stereo system, you should probably choose the larger model.