Hiring a ModernizrJS developer is beneficial for your project as they can help create a seamless user experience across different browsers by detecting features and applying fallbacks. They have the skills to ensure your website is responsive and accessible to all users, regardless of the technology they use. Their expertise will improve the compatibility of your website with various devices and browsers, enhancing user engagement and satisfaction. Additionally, they can help in reducing the time and cost associated with cross-browser testing. This ultimately results in a more efficient, user-friendly, and successful web project.