Simple and Intuitive - The Price is Right Simple and intuitive. Great video to document how to use the tool. You might clarify in the app that a high and low duct pair only counts as one opening. A results screen showing the detailed calculations would be useful for cranky inspectors that want to see that calculations were actually performed, and not just ball-parked.
Quick and Easy Gives a quick idea as to whether more air is needed, and if so the solutions are pretty cool too.