The problem, which people in medicine know full well, was the fact that blood is highly variable depending upon when and where you take it. It's why you have to take so much to get decent lab results.

A "fingerprick" was always going to be ferociously unstable.

It could have had value if taken repeatedly. I would be far more inclined to monitor myself if I had to only give a drop every 3-4 days. That way you could spot trends.

However, that was never going to produce a unicorn.