I am not sure what type of cycling you do, but many of my longer rides would end up draining the battery on both my iPhone and the watch. Also, my speed/cadence sensors are ANT+, so I would need to replace those to pair them with the iPhone. Lastly, I need instant data, especially heart rate, time, and cadence, and currently the

Watch would have a hard time reliably displaying those due to lack of apps at the moment (that should change quickly) and, again, battery life. I also am curious how the screen would do in direct sunlight. Maybe in a generation or two it can be on par with a tri watch, but I don't believe it is now.
I keep coming to the same conclusion with the

Watch and fitness. If you are looking for a glorified step counter, it is fine, maybe even fantastic. As a replacement for a Garmin fenix, 920XT, 810, 510, 500, etc., I think it has a ways to go before it is a real contender for those who would be interested in those devices. In my opinion, the

Watch is a fashion-focused smartwatch that happens to have some fitness features.
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The optical HRM to this point have required a tight fit to be accurate. Even then, the accuracy varies.
EDIT: Another thought. No mounting system means you can't always get the information you may need when you need it.