What a load of bullshit.
Serious users would almost certainly be more than happy with a simple graduated scale which changed colour alongside the scale to show the current value.
For example blood glucose on a scale of 3 to 12.
I assume this would work nicely with a smart watch (or other bracelet) with a light source and camera to continuously record the values; first obvious problem is keeping the camera located in exactly the right place. Certainly good for scanning with a mobile phone app. Very good as a medic alert tattoo when an unconcious (or mentally wandering) diabetic goes low or high. Hypo or Hyper with suitable instructions highlighted.
I would be happy with one on the back of my hand showing blood glucose and blood ketone levels. Biggest task would be to source some backless cycling gloves.
No doubt Big Pharma would make sure you had to renew the tattoo every month just to keep the revenue stream nice and active.