Financially, even if self funded, Libre is cheaper: for Dexcom you need to fund the receiver and transmitter as well as the sensor.
Functionally, Dexcom is richer than a standalone Libre because it can be used to alarm when it detects a BG out of range (too high or too low) or changing (going up or down) too fast. However, some geeks* have pimped their Libre to provide this capability.
Aesthetically, the Libre is smaller but it is only licensed to be warn on the arm whereas the bulkier Dexcom can be hidden on the belly.
Accuracy-wise, both measure interstitial fluid rather blood glucose which tends to be delayed about 15 - 20 minutes compared with a finger-prick test. The Libre is factory calibrated whereas the Dexcom is calibrated twice daily with a finger prick. Personally, I prefer this as it learns how your interstitial fluid differs from your BG.
However, I found neither to be close enough (or consistently different) to finger pricker for me to justify the expense.
Many find either brilliant - I guess it is a case of body-type, life style and sensitivity.
I trialled the Dexcom G4 because it is compatible with my pump. But have heard the G6 is being developed and soon to be released.
*I mean that in a friendly, non-derogatory way
