Heart rate variability requires more accurate measurement than a simple pulse measurement. I believe that some of the (older?) consumer heart rate monitors can'

Heart rate variability requires more accurate measurement than a simple pulse measurement. I believe that some of the (older?) consumer heart rate monitors can't do HRV, so it'd be surprising if the iPhone camera hack could measure it reliably. HRV is a pretty good measure of how stressed your body is, looks pretty useful for fitness training and illness/injury prevention.