The long answer is pragmatic. While the cost of Duet Display ($9.99 one-time for basic, $19.99/year for Pro) feels steep compared to a "free repack," the hidden costs of a repack are astronomical:
– The modified app must be signed with a valid provisioning profile and developer certificate, otherwise iOS will refuse to install it. Tools such as TrollStore, AltStore, Sideloadly, Esign, or Scarlet are used for this re‑signing step. duet display ipa repack