Cluster Rocket I

The reason to pick the first tier over the second is that it will not chew through terrain. You can fire it inside an arena, a farm or your own base without repairing walls afterward. The trade is losing the digging utility, which almost nobody wanted out of a combat rocket anyway.

The initial blast is wide, and the fragments that spray out bounce off surfaces before popping. Against a single boss most of that is wasted: the fragments share invincibility frames, so they queue behind each other instead of all connecting. Against a packed screen during a Lunar event or an invasion, the extra pops find separate targets and the ammo earns its price.

Only a few launchers respect the cluster behavior. Fire these out of anything else and you are paying a premium for an ordinary rocket. If the cost stings, Stynger Bolts do a similar job for a fraction of the money, provided you are willing to commit to the Stynger and nothing else.