borutg:
Does this shield allow you to have an uninterrupted power supply and the LiPower source only during the absence of external source?
Power should never be drawn from a LiPo while it is being charged. For this reason there is (or should be - see the microchip datasheet for the charge controller) a P-Channel MOSFET that bypasses the LiPo when there is external power available.
When there is power, the power is split between running the Arduino and charging the LiPo.
When there is no power the LiPo discharges into the Arduino.