This is a neat idea and one I was both surprised and excited to find in the app store when I was looking for such a thing. Sadly it fails in implementation, it just doesn't work terribly well, I almost wonder if they are just faking it and have some heavy bias to report 80 bpm, since that's believe for most.

But in my experience at least, when you compare it to a real heart rate monitor, it is always quite off.