I have the rubber flappers on mine. Do you need them? That is a question for you. How comfortable are you about not getting a wave/wake slamming the back of your boat at idle and shoving water into your motor when it isn't running? When the motor is off there is nothing keeping a blast of water from going right into your valves. For me, it is just added insurance to water reversion. I have too much money rapped up in my motor to take a chance. Just my .02.