The Dexcom G6 is the best CGM on the market, but its sensor filtering (Kalman or particle?) has smoothness and/or continuity priors that cause persistent inaccuracies.

I observe these persistent inaccurate states on the fifth or sixth day using a sensor. Calibration doesn't help. The reading goes wrong and stays wrong.

It probably happens to you, too, but anyone who doesn't test with a glucometer will likely not notice the failure. You will be harmed by these inaccuracies. Persistent inaccuracy is different than the Gaussian (normal) error of a glucometer, which is far more benign.

Also, CGMs are slow. The reading is based on interstitial fluid and lags direct blood glucose test by 15 minutes or more.

I have completely abandoned the Dexcom G6 and have gone back to 16x daily finger stick blood testing. I am also on a low-carb/high-fat diet, which makes it easy to maintain normal human blood glucose. My HbA1c has been 4.9 for a decade.

I was overjoyed to use the CGM at first, but it turned out to be a net loss. If you want to control your diabetes, use a glucometer and adhere to a strict low-carb/high-fat (ketogenic) diet.