The current state of the technology is probably best described as "finicky": the sensor skin patch needs to be replaced every week or two, at which point it's much less accurate for a couple days. It also needs calibration inputs from a finger prick at least every 12 hours. In general if the sensor is reporting a high or low condition her first action is to double-check with a finger prick. More often than not the sensor is simply wrong.

With all that said, it's better to have the sensor than not. She is able to use an app [0] to track her glucose levels over both the short term and long term trends. She's been able to use that data to make dietary decisions which allow her to keep her glucose within range and she had very good A1c levels (5.4, vs a goal of "under 7" for many diabetics) at her last checkup.

I think the long term data collection ability means that a more connected sensor (as opposed to the linked tattoo) will continue to be beneficial for diabetics. The next steps in the useful technological development will be to integrate with insulin pumps (this technology is already in trials) and to integrate with diet tracking data e.g. from MyFitnessPal to assist with meal decisions.

0: https://github.com/StephenBlackWasAlreadyTaken/xDrip