Using fitbit flex and polar heart rate monitor

HELP!
So I've been using my heart rate monitor to log my workouts on MFP for sometime now. My hubby just bought me a fitbit flex though. Now I'm confused about what to do. My fitbit is synced to MFP, so should I wear it while working out? Or should I take it off? I still want to wear my heart rate monitor as I feel like it will give me more of an accurate reading while workoing out. I'm confused as to what will happen when I record my results of the heart rate monitor. Will it double count all the activity? Any advice? Thanks!!