Speechify and Avocado both turn text into speech, but for different reasons.
Speechify is for listening
Speechify’s main app reads things aloud for you: web pages, PDFs, emails and books, at whatever speed you like, on your phone, in your browser or on your computer. Premium unlocks a large library of natural voices. For making voiceovers, Speechify has a separate product, Speechify Studio, with its own plans.
Avocado is for making
Avocado is a studio for producing voice audio you keep. Write a script, pick or create a voice, generate takes, direct the delivery, and export the result as a file. Voices are made on your Mac with open models you add yourself, and the app is free.
The short version
To listen to your reading list, choose Speechify. To create narration, dialogue or voiceovers on your Mac, choose Avocado.