FitBit Calories Burned Against Food Cals in MFP

The problem is that you will be looking at an incomplete picture: your total calories burned is only definitive at the end of the day. For example: if you check at 6PM, 6 more hours of BMR calories are still missing (on top of any potential activity calories). In the given example of 6MP, that's around 400 calories for me that would be missing from the total calorie count for the day at that point (more for you or less depending on your personal stats). If you don't mind some mental math to take that into account, it would certainly be a valid strategy.

For incomplete days, MFP calculates a projection of how many calories you will burn for the entire day. But that also has it pitfalls: if you are very active at the beginning of the day and less active later on, you might see your calorie adjustment decrease as the day goes on.

Also MFP shows you your calorie goal including the rate of weight loss you chose. Looking at the Fitbit total number of calories burned, you would have to subtract the deficit you're aiming for. Again, not problematic if you know the numbers and don't mind mental math (losing 1 lb a week is a deficit of around 500 calories per day).