Like the Makeshift M60, there are better versions of the RAT4 in Far Cry New Dawn.
By the time you’re able to unlock them, you’ll probably not be needing explosives. Explosives are good early on in New Dawn, but once you unlock a few great snipers, there’s rarely a need to engage on such a bombastic level.
That said, the Makeshift RAT4 is excellent for taking out enemy convoys, blowing up squads that are camping by cars, and generally causing mayhem. The Makeshift RAT4 packs a hell of a punch, so it’s a great bazooka to carry around with you early on.