Faster typechecking for Python is very much needed. But this project seems like it was built in a hackathon -- it is not a true standalone typechecker.
My research agrees with your assessment. While I'm sure it's a lot faster (I think the README implies it's one or two magnitudes faster) it just doesn't sit right to me that it's essentially just transpiles to Erg and delegates the actual hard work to the Erg typechecker. This works, but I feel like it fundamentally limits what Pylyzer is capable of, and how much control it really has over the underlying type checking process, as to it, the Erg type checker is essentially a black box.
It's a wrapper (a non-trivial one, to its credit -- especially considering everything is a wrapper if you look at it the right way -- but still a wrapper) rather than an actual full solution.
There's also really only one maintainer (who seems to do a decent job, but I don't seem to recall much more than just bug fixes). Makes me hesitant to really depend on it sticking around long-term or having features that meaningfully progress in the future.
If you're already making that then building a type checker wrapper on top of it makes perfect sense.