3how cluster rockets behave
Impact throws shrapnel and every fragment detonates on its own. Against a pack of enemies that is a lot of extra hits from a single shot. Against one large boss most of those fragments land on empty air and do nothing for you.
the tile damage matters more than the numbers
This is the digging version of the pair. Each secondary blast tears terrain as well, so a burst that misses can chew through your arena floor, cut a rope you were climbing, or drop you into the lava you were fighting over. Keep the non-destructive version for arenas you built and want to keep, and save these for open ground or for when tearing up the room is the point.
buying them
Stock is awkward. The Cyborg only lists them while a Blood Moon or a Solar Eclipse is running, and only once Martian Madness has been beaten, so buy deep when the window opens instead of assuming they will be there the next time you need a few.