I have flat feet as well. No orthodics will ever change the shape of my body, but they will kink it and cause problems somewhere else if not with my feet, particularly when working under loading, lifting or running.
My body took 27 years to take the shape it is now, plastic inserts for my shoes will only cause problems.
It's surgery (if possible) or play the hand you were dealt. Flat feet suck for running but make you a gun in the water if you get your technique down.