Order them in pairs. A flash takes two and a half batches of gun powder, so one leaves half a batch lying on the bench, while two use the batches exactly. That is why the calculator charges the same sulfur for one flashbang as for an F1, and far less than double for two.
The heavier line is the metal fragments. A flash takes more of them than an F1, and frags are also your doors and base upgrades, so a box of flashes is never as free as the sulfur makes it look.
Craft them for a planned push, one or two per player, with an F1 to throw in right behind. On a roam they do little; out in the open a smoke grenade is the better throw.
