I don't have a fitbit, but from what I have read...BMF takes more into consideration when calculating calorie burn then does a fitbit. The fitbit doesn't have the same technology built in as a BMF so it only records certain data. I would go with the BMF.

my BMF is always 150-300 cal higher than my fitbit, but the steps are lower. I'm confused at which one to believe for the inactive times. It's obviously more accurate in that it measures the intensity of your steps ( i.e. stairs vs flat steps).

I'm still afraid that my metabolism is ruined from VLCD to use it for creating my deficit!

I've wore both the BMF and FitBit together for over a week this winter. Alot of my winter activity is not step related (I raise cattle - spend alot of time cleaning barn and grinding feed in winter) and the FitBit regularly recorded 30% less calories burned than the BMF. The steps however were typically w/in 600 (I'm typically over 10,000 steps/day) w/the Fitbit being higher. I have worn them together once or twice since spring started (when my activity involves more steps) and they are closer in calories but the FitBit is still at least 15% lower. I totally trust the numbers from my BMF -- it has been extremely accurate for me while losing (3 months) and during my maintenance (2+ years)..