This adapter (or dongle) basically enables your iPhone to accept an ANT+ signal. The result is you can use your Garmin ANT+ accessories such as the heart rate strap, speed/cadence sensor or running footpod with the Garmin Fit iPhone app. The Garmin Fit app turns your iPhone into a powerful training tool. The app (downloaded separately at a nominal charge) provides current speed, distance traveled, route traveled and calories burned. You can review your stats at a glance or later thanks to automatic uploading at Garmin Connect.
Please note ANT+ adapter is not compatible with the Wahoo Fitness dongle or applications that support the Wahoo Fitness dongle