This is the kind of module that 99% of Perl users will probably never directly need to use, but is a vital dependency for things like Moose to prevent them being slow. (Or at least, prevent them from being *hideously* slow.)
I started using it in Type::Tiny quite a bit, but was deterred by its use of Sub::Exporter, which although itself a great tool, introduces quite a list of dependencies, which would have been inappropriate for a "*::Tiny" module.
I ended up re-implementing most of Eval::Closure as Eval::TypeTiny and bundling that. Nevertheless, in future projects I'd still certainly consider using Eval::Closure, especially if the project already had a direct or indirect dependency on Sub::Exporter.