A Mithril.js developer can be a valuable asset due to their expertise in this light yet robust JavaScript framework. They can create highly efficient, high-performing applications with smaller file sizes, which can improve load times and overall user experience. Their knowledge of Mithril.js' unique features like routing and XHR utilities allows for the creation of sophisticated single-page applications. By hiring a Mithril.js developer, you can benefit from their ability to code complex functionalities with less code, leading to cleaner, more maintainable codebases. They can also leverage Mithril's flexibility to integrate with various other technologies as per project requirements.