Poor fit and terrible design - Crimson Trace Green Laserguard for S&W M&P Full Size and Compact

first off the unit is difficult to put together unless you have three hands. Since it comes in two parts, you must hold one side, then snap the second half onto the first part, which would work, IF the parts fit the pistol. It does not fit into the grooves of the rail but sits upon the rail and not in the groove. Appears the laser was not engineered to specs of the S&W 40 rail. Had high hopes from the reviews but obviously reviews are fake or I got a fluke. Will return.