It appears to be JIT'ing, so presumably a significant performance difference compared to not JIT'ing. If you mean compared to a JIT with multiple backends, presumably not.
EDIT: Here's an article about PJIT that compared it to Emu68 that gives more info: https://www.buffee.ca/Why-PJIT-Why/
Documentation files seem outdated. Repository seems a bit low on information. Are there any unit tests too?