1. No heart rate accessory ? Without that, I don't see it having significant impact.
2. Also if you need your smartphone to provide a screen for the GPS to work, it kinda makes the screen redundant.
3. As for mountain bikes, would have been interested in knowing if it had a trail application to go along with it.
4. Again, for the mountain bikers, how's it stand up to shock and vibration, for those frequent tumbles and trees that like to jump out in front of you ?
http://www.polar.com/us-en/products/compare?product1=83988