As an example: I was on a study that gave T1D patients Dapagliflozin (Farxiga). During the study, while on a long hike, I was hovering at low sugar and consequently insulin supply was mostly cut off for an extended period. As I started to to feel unwell, I measured ketones. I was briefed as preparation for the study to measure ketones when something seems wrong. Otherwise I wouldn't have thought of measuring ketones. Might not even have carried the kit.

On that occasion, the ketones were way above 1 mmol/l: a very high value. Protocol would have required me to call the study doctor due to the high level. Since it was a Sunday, I spared her, shot some insulin, ate a sandwich, and continued my hike. I could do that because I was not alone on that hike. I knew that if my situation deteriorated, somebody would be around to call rescue.

At the study debriefing I mentioned the incident and they said that adding to the effect of the Dapa, I was probably dehydrated, which led to the rare situation of both low sugar and high ketones.

All in all I think that if the sensor makers exhaust possible improvements for the glucose, it can make sense to add the ketone measurement as a safeguard. Having high sugar can have many reasons, and it often takes me a while to get to measuring ketones. Getting the signal of rising ketones, I would react faster a few times a year in situations where my insulin supply is broken.

All this device adds is a simultaneous ketone check, which is really only relevant to diabetics and not as much of a benefit because ketone levels are often checked with a urine test.