The truth is that, today, if I was going to use a tool to generate voices (say for YouTube), I wouldn't necessarily pick a small SaaS tool. I'd use Amazon Polly or some other GCP-style platform voice creation tool. There are already a few products in the space, and their costs are so low as to be almost negligible (example: Polly, 5 million characters free). For a commercial project, I could probably stay on a free tier for a whole year.
With Dall*E, it seems like the only option, and it's such a superior option that a website could abuse it for commercial profits. But for voice synthesis, it's already dirt cheap and commercially available without limitations.
15.ai seems to beat them on some sentences, but not all. Looking forward to the day when we can have real human-level quality of voices on-demand.
The whole history behind the project is fascinating: 4chan had a huge role in its development, and the project's work was stolen by an NFT company that a famous voice actor endorsed not too long ago.