I'd be curious to see what your take rate is. I imagine 99.99% of casuals are just going to close the window and leave when they discover this is a paid service, which you hide up until they need to enter a payment method.
Thank you so much for the comment. Text-to-speech costs $16.00 USD / 1 million characters[1]. So if an article has 5,000 characters, it costs 0.08 USD. If you put 20 articles, it costs 1.6USD. And current my assumption is most of the articles contains more than 5,000 characters.
[1] https://cloud.google.com/text-to-speech/pricing