$ vs tactical use...
$ or prices may be an issue too. A Surefire foregrip 12ga whitelight costs nearly as much as a NIB 870 12ga! The same goes for a cool Viridin green laser aimer/light. They run almost as much as a NIB M&P or XD series(pre Sandy Hook/gun mania 2013).
Unless you are rich or are a SWAT cop or DEVGRU SEAL I doubt you can "kit up" that way.