Killhouse 551 Mock Holographic Black
Due to their near immunity to parallax distortion, Holographic sights like the 551 Mock Holographic Sight have an huge advantage over regular red dot sights. With a red dot sight your eye needs to be in line with the sight to line up the reticle with the target.
If your eye is not lined up, your shot will end up being off target. With the 551 Mock Holographic Sight, you can move your eye off the sight line, and the reticle will stay on target. This is achieved with the way the reticle is projected onto the lens and why holographic sights are superior to basic red dot sights.