Bigger than you would think. - 3EIR DIR Green Laser Sight

I also own the smaller version of this laser. That said, this one is much bigger, and when mounted on the top rail, it's quite wide, making cleaning a door something you have to think about. The lasers are easy to zero and have stayed true for over 500 rounds of 556. The one I purchased did not come with a switch. It works with Surefire pressure switches, which is an added expense.
It's much less expensive than my Eotechs. They are also much lighter.