I know someone who had a 2 week trial for a CGM (no idea what brand it was). They removed it after a week because the numbers weren't even close to finger prick numbers.

In this particular case it was useful in that it at least showed there were no random overnight spikes (which could have led to a high A1c from some months ago), and even though the numbers weren't anywhere near the same as finger prick tests, they were consistent in their difference: Off, but by the same amount (percentages?) all the time.

My guess is that unless there's a similar case where you're trying to figure out if there are blood sugar spikes or lows for some reason that you're just not picking up with the timing of eating and finger prick tests, then you probably don't need one.