The rivet cutter has been separate from the staking set. If it is now included in the set that is news to me.
The cutter has a hole in the middle of it so that the post of the rivet will not be harmed. The cutter only removes the peened portion. The cutter might prevent you from replacing one rivet, which preserves the external appearance of the receiver, but is not a mandatory tool.
The staking set, whether purchased or made, is needed.