Exercising while wearing Fitbit and Polar M400

Schila64

I have the app for the FitBit and the Polar M400 linked to MyFitnessPal. I use my Fitbit while I'm jogging on the treadmill. When I finish, I see that on the exercise part I have logged the steps that the FitBit records and the exercise that the Polar app records. Is this right or should I use only one?