On Shusher and X. swarm:

Shusher

CMC: This in important for two reason: 2 mana > 1 mana, obviously. But you may reveal shusher with ADN getting an extra damage.
It`s ability is needlable and stifleable but it's uncountereable and makes your spell uncountereables if you have the open mana. In this point if feel shusher like a "sphere effect".

X. swarm

CMC: One mana is one mana.
Its abaility is mana independent and not needleable. However it's countereable.