I used the libre 1 very happily until I started to develop and allergy to the sensor. Unfortunately that also meant that the results became wildly inconsistent. Abbott to be fair sent me numerous replacement sensors and even a new reader. Eventually I had to conclude that my body didn't agree with that piece of technology and went back to testing (8 times a day, because my hypo awareness was impaired).
For the last 2 years I have been using dexcom. The alarms make all the difference to my hypo awareness (I get warned before hypo levels so I get less hypos and hence my hypo awareness has improved). It's not perfect and occasionally I get really weird results, sometimes it reads low for no reason and I do need to check it against a glucometer occasionally, particularly of hypo. And I do occasionally get a bad sensor. But for me it's as life changing as my first glucometer back in the 80s.
I think you have to recognise that the sensor technology is sensitive to any reaction your body has to the filament and may not suit some people. I definitely need a glucometer as a back up, because some sensors are inaccurate, and if I'm having a serious hypo, the sensor time delay means I need the glucometer to check when I start to come back up.
As for hba1c predictions,
@Seacrow makes a very good point about the lifetime of red blood cells meaning that people with identical bg results can have different hba1cs, and I personally think TIR (time in range) is more important, if you're using the technology that calculates that. I notice that my dexcom was under-predicting previous hba1cs but they have recently changed their algorithm, It will be interesting to see how my next hba1c compares.