The FastFire M3 can be mounted on either the left or right side of the T.M.P.R. Sight. The FastFire M3 comes with a mount that allows it to be used as a "regular" FastFire 3, separate from the T.M.P.R. System. The FastFire M3 can also be used on a pistol, mounted solo on shotguns, etc. Automatic brightness sensor adjusts brightness to match the environmental conditions; also has 3 manual brightness settings.In addition to using the T.M.P.R. central battery, the FastFire M3 has its own battery, like any other FastFire sight. Battery access is conveniently located on the top of the sight; automatic time-out feature after 8 hours helps internal battery last up to 5 years.