Matthew Moskovciak of CNET says, "Now that the Fitbit iOS app can track my steps using the built-in M7 chip, I've stopped carrying my Fitbit Ultra. And that's a warning sign for the emerging wearables category."
If you are a dedicated fitness buff, wearables will always be attractive to you while jogging, skiing, competing etc. I can't imagine many runners carrying an iPhone while competing in a marathon. But that's a very limited number of people.
For the average person, an iPhone 5s with any number of free apps can do almost as good a job as a dedicated fitness tracker. As he says, it should raise red flags for the companies involved in this market. http://reviews.cnet.com/8301-34900_7-57617416/how-the-iphone-5s-replaced-my-fitbit/