Your example is overly optimistic - if it was consistent like that, you'd just adjust it at the factory or calibrate it later on, and you'd have a perfect instrument. In reality, the data is all over the place, with a large spread. You might still be able to get some kind of weak trend out of it, if you knew the tendencies of that particular equipment. I doubt you could even take long-term averages and rely on them.

Take for instance an elliptical machine I own (it's about 4-5x the price of the cheapest ones, so I guess we can call it "mid-range"). The heart-rate monitor on it is almost worse than useless. Sometimes it will report 200 BPM when I'm not holding the sensors. Sometimes it will under-report for long periods (e.g. reporting < 120 in the middle of a session, where I'm fairly confident my actual heart rate is around 150). I would not recommend relying on these things much.

That said, I think the general idea is not a bad one; we could definitely use more data to analyse. It's just that equipment that gets sold to the public is pretty erratic at the time of writing.