I used a Mio with my Garmin 500 and initially loved it, then hated it. It's great to wear, much better than a chest strap. But it quite often lost the heart rate, under reporting for 5 minutes at a time by 30-50 heartbeats. Then it would jump up to actual for 10 minutes. It really doesn't work well below 40ºF. I sold mine & go without HR and don't miss it at all.