Well... that depends on whether or not Flandre is more or less running the show in the fusion, or the others have some mitigating effect on the gestalt personality.
SDM fused? We are all in trouble now...UNLESS they gained Patchy's weak self + asthma attacks...we might be able to escape then. If they also gained Meiling's laziness and Remi's Charisma-Break tendencies, then we should be all fine.