I goofed around with a sheet of photography film (used to change the color of flash light) and the black/white swap function o my iPad, and it was tolerable but wasn't nearly as good as a true NVIS compliant filter. The ghetto system would work fine for instrument approaches because who cares if the colors are off, but if you needed true color representation the NVIS filter won't alter the colors, so red will still be red, etc. The NVIS filter will also make it so you can stare at the filtered screen and not bloom your goggles. All that said, it isn't all that hard to just manage where you shine that screen and put the stupid thing away when it will be a distraction.