Yeah it is very cool! That is why I sucked it up and spent time learning this language despite not really giving a damn about yet another pure functional programming language. But that whole new way of writing software. That is something worth exploring!

About performance. This system doesn't really affect the performance of the language. There is no build time to speak of if that was your question. Builds are incremental. Every time you commit a function it is compiled and stored in an essentially compiled state.

If you are asking about performance when Unison runs I don't think that is anything awesome at the moment. They are not focused on a fast implementation at the moment but just hashing out the language and the whole system. I believe Unison currently runs on an interpreter, but that is just a temporary solution. It will be compiled to machine code in the future.

The language is similar enough to Haskell and OCaml that I think you will get performance similar to those languages. So quite fast but not quite at the level of systems languages with manual memory management like C++, Rust and to some degree Go.