I have an iPhone 4S running Cyclemeter paired with a Wahoo Speed and Cadence sensor plus a Wahoo Blue HR. No dongle required, all by Bluetooth with the phone. If you already have an iPhone 4S or 5, I highly recommend. I have never used a Garmin so I cannot compare. I am very satisfied with Cyclemeter. More there than I will ever use. Speed, distance, cadence, HR, maps are all very accurate. Elevation works pretty well also if you are on well traveled roads. Many graphs and custom layouts are available.