Apple Watch and map my fitness

Does anyone use Apple Watch and Map my fitness to sync back to My fitness pal? I want to use Map my fitness to track my walks, hikes, jobs, but want to make sure it doesn't double my exercise or calories burned by also getting info from Apple Watch/health app. Plus, want to know if heart rate meter in Apple Watch is used to calculate calorie burn if using Map my fitness and not Apple fitness tracker feature. If you have experience with this, please let me know and have a discussion. Thanks