A developer documents their experience using LLMs (Grok 3, GPT-5, Gemini 2.5 Flash) to create a cross-platform Elixir NIF in C for disk space monitoring. The project aimed to provide on-demand disk usage statistics without relying on Erlang's os_mon service. Through iterative code reviews between different LLMs, they successfully created a working package that supports Linux, macOS, Windows, and most BSDs, though with some limitations on older OTP versions. The author provides candid insights into LLM capabilities and limitations, noting issues with overconfidence, inconsistency, and the need for significant human oversight in the development process.