Well, yes and no (althought the question is a bit open).
It's more or less beta quality, and very primitive. It's discouraged to be used with Rails, so I'd be inclined to state that "we didn't get it yet".
I'm also personally skeptical that the unusual approach (invoking a whole C compiler in a separate thread) will stand in the long term - but that's my own take.
The CRuby JIT is stable but whether it improves performance or not is workload dependent.
It's simple not primitive. MJIT is designed to take advantage of a C compilers optimization.
"Compile to C" worked for Chicken Scheme for the past 20 years and continues to be a popular way for functional langauges to compile. It's also how Nim works. It's all about different trade-offs.
Are there any benchmarks available? It seems I can find very little (OptCarrot, some microbenchmarks, and some general assessments about usage with Rails), and a broad(er) overview is crucial to assess the overall performance (I suppose that you can have workloads where the performance degrades).
It's more or less beta quality, and very primitive. It's discouraged to be used with Rails, so I'd be inclined to state that "we didn't get it yet".
I'm also personally skeptical that the unusual approach (invoking a whole C compiler in a separate thread) will stand in the long term - but that's my own take.