I started using the C25K app on my iphone 6 earlier this week. One little thing that I wish Zenlabs would improve is the pause button; either making it where you have to press and hold, swipe it, or double tap it. Tapping it once makes it very easy to accidentally pause the workout if you put it in your pocket when you run.
Other than that, the program seems to work well. I will likely upgrade it to the paid version soon.
Thanks,
J White