A Mean.js developer is equipped with knowledge in MongoDB, Express.js, Angular.js, and Node.js, forming the MEAN stack - a complete set of JavaScript technologies perfect for building dynamic websites and applications. This full-stack development tool allows for quick, efficient development processes with high performance. A Mean.js developer can handle both front-end and back-end development, reducing the need for multiple specialists. This can streamline communication, improve consistency in the project, and potentially reduce costs. Additionally, JavaScript is widely used, ensuring a wealth of resources and community support.