I've been using this app regularly while I commute to work by bicycle over the past year. The app has turned out to be useful at tracking my weight, blood-pressure and pulse. The app has been reliable, without crashes, while in use about 3 times per week on an iPad 2. My employer pays me a small health incentive each month that I get in 12 or more qualified workouts, but I find the app actually useful and fun to use.
Because of the size of the iPad I run on, I haven't purchased the heart rate sensor in-app option or matching hardware, since that requires bluetooth, which is a line of sight technology, and the iPad rides in my backpack inside a pannier on the back of my bike. I suspect a heart rate monitor on the front of my chest is not going to have a reliable connection with this setup (although I admit I haven't given it a try because of the cost of the equipment). I'm also not going to mount an iPad on my handlebars or strap it to my arm the way you could do with an iPhone.
I do suggest to the developers that they add the ability to recall past workout descriptions (over 50 times last year I entered "Commute to work" in my bike workout entries).