It’s not a script, it’s a codebase which you have to compile as you would compile the official KiCad if you would download the source code.
The history of that “branch” is notoriously sad. The author wasn’t capable of co-operation and created that code base in a strange way. I think it’s not up to date at all but is several years old except for his own changes.
The current nightly builds support curved traces. It’s not perfect yet (or even especially good as far as the UI goes) but you can create curved tracks by selecting a corner with two segments and select context menu -> Fillet. However, the nightly builds are still unstable and curves are not well tested.