I have used a number of different CGMs and found the best ones for me were the ones which I could calibrate. Its as if the “man in the factory“ against who the Libre was factory calibrated had a different physiology to me somehow that meant the interstitial fluid readings ti blood glucose readings algorithm didn’t quite match.
Therefore, I found one of the unofficial Libre apps like xDrip or Shuggah which I could calibrate with my finger pricks rather than the finger pricks of the “man in the factor” gave me a more reliable readings.
i try to calibrate when my BG is flattish and at “normal levels”, For me this was the start and/or the end of the day. After the first day or two, the calibration only nudged the app readings up or down less than half a mmol/l but it gave me peace of mind during the rest of the day.