Ok. Let me ask differently. Why would I download and use LLVM for working with java code? Which usecases favor this?

It's more an fun educational overview of the new FFM API.

I can't think of many actual use-cases where you'd want to use the LLVM JIT over those built-in to HotSpot.

Interfacing with existing LLVM-based systems, writing a very tight inner loop using LLVM where you absolutely need LLVM-like performance, or creating a compiler that targets LLVM using Java would be the main "real-world" use-cases.

This is interop glue to cross language boundaries in the JVM without the problems that come with JNI. The natural goal/use-case being that you can call pre-existing code in other languages that target LLVM IR.

That's not what the article is about.

The article is presenting something different entirely. This is the precursor to what it would take to create a compiler written in java that produces native code.

"why would I use a frying pan when I can use a flashlight"

The two things have nothing to do with each other.