I discovered and tried to use this feature to turn an older iPhone into a dumb phone for myself, but hit several blockers

  1. It’s incredibly slow to transition in and out of the mode, as mentioned in the article, which made setting it up (constant tweaks) very painful
  2. For messages and calls, you were limited to select contacts only. So I couldn’t just text/call a number when I needed to.

They may have polished the feature since then, but given that it’s an Accessibility feature and was never meant to receive much attention in this regard, it may always be half-baked.