I received my Apple Watch a couple of weeks ago and have been using it with my cycling workouts. I already have a garmin GPS system on my bike so I have been comparing the results. The HR seem to track pretty well with the Gamin, but the calories burned seems to be about 25% less than the garmin. While running the Activity App in the outdoor cycling mode, you have three screen you can look at while cycling, one shows distance traveled, one shows speed, and the other shows HR. Sometimes when I have the HR screen on, the HR is updated instantly and at other time it says it is acquiring HR. It can take 20 to 30 seconds to get the reading when it is acquiring. It seems to be very accurate with speed and distance traveled. It should be since it is using the GPS system in the iPhone that I also carry. While cycling the screen is off and will activate when you move your wrist to look at the screen, and it will show the data you have on the last screen mode set, HR, Speed, etc. The one downside is that it can significantly drain the battery when operating. A one hour ride will typically drain about 25 to 30% of the battery. I assume most of the drain is caused by the constant HR tracking, and am considering getting a bluetooth HR strap to see if that will lessen the drain. I think you can set it to not constantly get HR data, but I like to see my HR while I ride and train. Generally, it is not a replacement for the Garmin just yet, but it is pretty good for a first gen product. When my gamin craps out, I'm not sure I would spend the $500 dollars to replace it.
I haven 't looked into the integration with Strava, but it does put all the data collected into the iPhone health app, so any apps on the iPhone that can read that data and upload it to online tracking systems should work.
