Like with most power meters, oval chainrings will result in a measurement error. Due to the changes in velocity oval chain rings produce through a pedal cycle, the power will be skewed higher than with a round ring, which has a constant velocity throughout each rotation.
The error induced by some oval chainrings is approximately a 2% over-estimation of power. The amount of error depends on the ovality of the chainring you choose, and you can roughly expect a 1-4% over-estimation of power.
The more important aspect is the accuracy and consistency of the powermeter and it is less important If the powermeter is reading 255 W when you are actually putting out 250 W. If you are more comfortable riding with an oval chainring there will be no issues in terms of power measurement, just keep in mind that your power numbers may be slightly skewed.
Please note that our PRECISION PRO (dual) powermeters on Shimano cranks are not compatible with aftermarket chainrings from any manufacturer.