• Lasers create laziness. Shooters tend to become reliant on the laser and forget to aim.
• They are almost useless in daylight.
• They require batteries and if those die at in inopportune time, you're screwed if you haven't practiced with the sights.
• They're expensive.
• It's actually faster to get back on target with the sights rather than the laser.
• They give your position away.

Further, most lasers require an extra motion to activate them. In a defensive situation the last thing you want is an extra motion. The only laser on the market that doesn't require an extra motion, that I know of, is the Crimson Trace. They activate with a normal grip, but cost double what other lasers cost.

Lasers are great for training. Especially with dry practice. They help show movement as you press the trigger. For defensive purposes they are almost completely useless on a handgun and a waste of money.

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