After 3 months of use I just say that the tracker always overestimates the number of steps, or the look when I run. It is not very disturbing. Sleep mode use is interesting, and surprisingly fair enough. The heart rate sensor is also fair enough, as long as you put your finger, do not hesitate to take more time to refine the measure.
In short I am a little disappointed with the device that could really be at the top if it was a bit more polished. We should be able to enter in cycling mode for example, and edit / adjust any measures.