Although there is the option of negating Knightmare Mermaid instead on Chain 3 with Infinite Impermanence , negating Firewall Dragon is crucial to ensure that after Iron Dragon Tiamaton is Special Summoned and its (2) effect is activated in a new Chain, Firewall Dragon could not activate its (1) effect in response and bounce Iron Dragon Tiamaton to hand
Still, you will have to be really careful with any addtional effect(s) you give to the Ritual Monster if you choose to add this perk, as you could use, let's say, Releaser, Demolisher or Prognosticator Djinns for a Chaos Magician Girl that locks Special Summons, is untargetable and/or discards from the opponent's hand, in addition to the effects it already has
If you can bring two of them down, you've already won
Mainly, the staff versions of these cards are listed and theyre quite pricey
This is why Charizard cards are valued much higher than cards of similar scarcity