I'm very happy with Dexcom G6, readings are usually the same as finger prick tests, even when low (which isn't very often since going onto HCL) or high. If it varies it's not usually by much.
Previous to using Guardian 4 (very similar to Dexcom) I used Freestyle Libre and it was always so wildly inaccurate for me. The bonus with the Dexcom is like EllieM has said it is able to be calibrated so even if it is slightly out you can put in a blood sugar value to bring it more in line.
I am a Dexcom One user. I moved to from Libre to Dexcom as for me Libre was very inaccurate and I had numerous failures. I have had some issues with Dexcom but I have personally I have found it much better. One feature I like is the ability to calibrate it.