This user (Jorge) posted a great graph comparing the Dexcom, the Libre and hand-tested BG:
As you can see in the graph (sorry it is in mmol/l, 10 mmol/l is 180 mg/dl, and 80 mg/dl is 4.4 mmol/l), Freestyle trend is above and Dexcom trend is below, consistently, regardless of 6 calibrations (red dots). The shapes and trends do seem to resemble each other.
Sometimes the differences between the two are above 2 mmol/l , which is 36 mg/dl, enough to cause a false low. For example at around 6 pm, Dexcom was already signalling very low and Freestyle did only give a slight slow. Both Dexcom and Freestyle gave more than their quoted less than 10 % error, consistently…
However, Jorge reports that the opensource app Glimp coupled with the Libre got the best results of all:
And the most accurate of the two is:
A free app developed to read Freestyle, was only away by 0.2 - 0.3 mmol/l throughout the whole day!
Here is the original thread on tuD: http://www.tudiabetes.org/forum/t/dexcom-vs-freestyle-accuracy/64087. Many thanks to Jorge for giving permission to report his GREAT post!