Mine definitely gets off sometimes, and in particular, during the first few hours after activation - it seems to really need that second calibration. Even then I find it occasionally gets out of whack and can be off by 100 points or more at other times (I’ve had it get off by over 200 on the high side, not showing as high as I was when I had a bent cannula this evening, and also had it show me at 80 when BG was 40) - but not that often after the first day, and it tends to be more accurate the closer you are to normal range. I also had a bad sensor in my first batch that after an hour on the phone with them, they finally agreed was bad and sent a replacement, this will happen every once in a while.
I just switched to the MM CGMS at the same time as going to Paradigm 2 weeks ago after 3 years on DexCom + MDI, which also had the same issues occasionally. (With DexCom I got an entire lot of bad sensors earlier this year which had me having bad readings repeatedly for months, and they swapped out a few of them but wouldn’t do the whole lot, wanting me to go through customer service one sensor at a time, over and over. That, and the customer unfriendly way they handled the latest upgrade, pushed me to switch.)
One thing I’ve found creates big problems is bleeders - if you hit a vein and are bleeding when you insert the sensor, it really needs to settle down and stop bleeding for a few hours at least before you try starting it up (and it may not work at all and need to be pulled in a bad enough case).