We use the Cateye V3 which gives us our heart rate on screen. It only need s one sensor on the chainstay to pick up speed and cadence. We have found the heart rate a big benefit in balancing the work load. If I see my heart rate going up I'll ask my wife how her's is doing: sometimes I get a sheepish answer and the feel a power surge. It seems she can get lulled into low power output by the scenery.