Somewhat useful

Its sort of useful if youre objective is just to go as hard as possible every workout. But it provides no guidance as you go, so its not helpful for managing a training program with hard and easy days. And its completely useless if the app inexplicably loses contact with the monitor mid-workout, causing you to lose the entire workout. The app only saves data at the very end, when you click "End your workout". Anything goes wrong before that -- too bad. More than a little irritating, when it happens.
Also, the workout "sections" function is terrible. When sections are added, the pre-section portion of the workout gets truncated or at least its duration is inaccurately recorded, and there is no meaningful ability to review the individual sections of the workouts.

Plantofail about Armour39, v1.2