That is the great mystery of this thread.
There are different interests at play. Some people want to replace proprietary software, others software which leaks data, while others have a focus on anything Google specific.
There’s not an analysis shared of what all these applications do. It is of course possible to do some search query, but a lot of work (which not everyone wants to replicate).
So I recommend other people to log what they’ve done, and share their findings, with references. Don’t be shy 
As for your specific example. TTS works locally. It is speech to text which FAMAG do remotely (even though I would argue they don’t need to).