Coming from a FitBit Charge 6, I'm a bit disappointed in the AW S11 heart sensor. It takes a while to get a reading while it's "measuring", whereas the FitBit is always reading your heart rate and displays it on the face. It seems to be accurate, it matches the Fitbit bar a difference or a beat or two. When taking a measurement, it seems to take a few seconds for a consistent read to come through as well. It's like it starts off a bit erratic and then settles down.