re:
The app is preinstalled on the iPhone 4s and does also work, but it won't track your moves etc. because it doesn't have the M7/8
But it can't still be used for everything else, e.g. Showing data from other apps
Unfortunately there is a bug which apple tries to solve until the end of this month, which doesn't allow other apps to use the HealthKit; so until now it's not possible to import data from other apps. But you can enter data manually, like I did.