> Is this seriously quicker than just writing in a language that you know?

Yes. Well, it depends.

Most of the prompts specifying requirements and constraints can be reused, so you don't need to reinvent the wheel each time you prompt a LLM to do something. The same goes for test suites: you do not need to recreate a whole test suite whenever you touch a feature. You can even put together prompt files for specific types of task, such as extending test coverage (as in, don't touch project code and only append unit tests to the existing set) or refactoring work (as in, don't touch tests and only change project code)

Also, you do not need to go for miracle single-shot sessions, or purist all-or-nothing prompts. A single prompt can fill in most of the code you require to implement a feature,and nothing prevents you from tweaking the output.

It is seriously quicker because people like you and me use LLMs to speed up how the boring stuff is implemented. Guides like this are important to share some lessons on how to get LLMs to work and minimize drudge work.