The pitch is "use Claude Code without Anthropic limits." What's actually happening is you're getting GPT/Codex responses dressed up to look like Claude. Those are different models with different failure modes. If you picked Claude Code because you trust how Claude reasons about your code, this swaps it out silently. No indication at the UI level.
The ToS angle is what I'd worry about more. Anthropic isn't being hurt here, they're not serving the requests. But OpenAI is, under a Codex subscription that definitely wasn't priced for "act as someone else's backend." Using your ChatGPT sub as a proxy for a third party product is the kind of thing that gets your account killed. Could also expose you to liability, depending on how seriously OpenAI wants to push it.
The project's own disclaimer says something about how use "may be subject to the terms of service of third party platforms." That one sentence is doing a heroic amount of work.
If the real complaint is that Claude's API is too expensive, fair enough. But this doesn't solve that. It just shifts the bill and the risk onto OpenAI's infra and your account.