I have both the vivosmart 4 and the fitbit inspire hr. I have no issues with either working out or sleeping (I wear both at the same time while exercising and sleeping). The fitbit is quicker at picking up on my heart rate increase by a couple of minuets while exercising but in the end they have similar HR average and HR max while on the elliptical for 30 minutes. Either its the same or different by no more than 2 heart beats. Sleep tracking they both start sleep and wake within 5 to 10 minutes of each other. The difference is the length of stages. Sometimes the stages are close in time and sometimes they differ by 45min and that doesn't bother me but what throws me off is when one might say i was in a deep sleep at 1am and the other will say I was in light sleep or REM. Sometimes they correlate but most of the time they don't. Which sleep tracker is more accurate? The more accurate one im keeping and the other I will give away or use it as a back up.