The Asus 144hz 24" gaming monitors have 4 different sights built into the monitor itself, which does pretty much the same thing. In some planes you can move your seat way above the gunsight line, and flick on the monitor sight, which has always lined up perfectly for me.
This is from Asus's website, I usually use the red sight as the green disappears in terrain at times. It was a downer that their IPS 1440p 27" monitor deleted this function.