The sight mark red dot:

This is the one that looks like a small projector and screen. It has a knob under the back edge that lets you switch between 4 aiming dots. Mine did red and green dots, but I have seen only red ones for sale too. It ran on a cr2025 battery, and had a built in mount. This style of sight can be had for $40 used up to $165 (which you would need to be a moron to pay)

THE GOOD:

It was cool because it had 4 different reticules; I also liked changing between red and green on said reticules

You could co witness.

THE BAD:

It didn’t hold zero (mostly on the wind age) if you switched between the reticules, or even bumped the knob.

Not parallax free (your head needed to be aligned in the exact same spot to hit your target, usually overcome by using your front sight for reference)

It was a special kind of ugly, guns can and should have an air of beauty to them, sexiness even, and when you put a useless putrid blob on the top it makes the gun less appealing.

FINAL THOUGHTS:

This (and the many copies of it) are not worth your time.