I don't know, the name implies they target the RyuJIT, which is a state of the art JIT compiler. I feel in general games should perform really well on a JIT since they are predominantly performance sensitive in a tight loop. Dolphin also has a JIT if I'm not mistaken. The alternative is to interpret which in theory should have worse performance (though in practice there's definitely exceptions to that rule).

I think it should be possible to achieve predictable performance, though it depends on the qualities of the JIT, it won't work if it's constantly recompiling or allocating stuff that needs to be garbage collected of course.