The really nice part of Whisper is being able to use it offline and on-device, it seems whisper memos is uploading your audio and notes to a server of unknown security, confidentiality etc.

I like Aiko for on-device transcription both in macOS and iOS https://apps.apple.com/us/app/aiko/id1672085276

Whisper Memos uses OpenAI API. The upside is that it uses the largest model - that would take 2GB on your iPhone.