For the past several months, I've been toying with the S&W M&P40 fitted up with Crimson Trace Corporation's LaserGrip LG-660 and LightGuard LTG-760.
We're familiar with the LaserGrip for M&Ps. We simply remove the existing palm swell/backstrap unit and replace it with the LaserGrip. For this M&P40, which has been around here since the line was introduced, I set the Laser's zero to be at the top of the front sight at about 20 feet. As it's a red laser, easily visible in dim light but not outstanding in daylight, I'm more concerned with indoor distances.
The pair of laser controls is at the rear. The master ON/OFF is the bottom button and, for me, requires the use of a tool to get it pressed. The upper switch is the activation pad. The LightGuard is trim, no wider than the host pistol, has a master ON/OFF switch on the front of the unit at the bottom. A strip runs from the unit under the trigger guard to the front strap of the grip frame. The activation pad is there.