I wouldn't be - such apps are not regulated medical devices. Why should Apple be giving such things the okay? It adds an air of at least implied reliability for such tools, and that's probably not a good place for anyone to be in.
(Not to mention, at least for me, such tools have proven horribly inaccurate.)
Certainly, and it may actually be a red herring. I have a Polar and I believe it to be fairly accurate. My initial impression of a HRM-style app was the more gimmicky pseudo-pulseox LED flashlight and camera style. Apologies for the misleading!