I make an iOS app that uses this API heavily for transcribing diverse audio of varying bitrate and recording quality. The audio often contains music, multiple speakers, sound effects. SpeechAnalyzer almost always gets it.

It can struggle with proper nouns but will return something phonetically similar.

My main gripe is that it requires a separate model download per language. I understand the why they did this (to save disk space). But it makes multi-lingual audio hard to transcribe unless you know ahead of time the languages in the audio.

As an app developer the biggest win from using Apple's model is I don't have to bundle it in my app so my app looks much smaller. If a user has many transcription apps each one could have their own model. If Apple's model is used only one copy is needed.