What are the differences and which one protects the screen from cracking more?
IPhone deflector or capsule case?
If I understand your question. The deflector is your Screen Protector or Digitizer Protector. Its the adhesive plastic sheet that covers it. And the capsule case referred as a hard case or generically as an "Otterbox". Both to protect your screen. Protector helps prevent smudges, scratches and supposedly prevent the screen from cracking any further. Capsule case design for higher abuse, like dropping on the ground which cause the screen to break. Usually comes with a deflector.