Heart Rate Monitor

For the Mio watch, it really depends what type of workout you are doing. I have used both the Mio and the Polar HRM, and have found that the Mio is reliable for both HR and calories if you are doing a steady workout (ie, running, walking, swimming, biking). I found that it did vary when doing intervals, because it is not taking a steady measurment...

But that's just my preference..most people I know do prefer the chest strap - the strap itself just bugs the heck out of me!