The experience of a React Developer in developing applications using React can be diverse and extensive; from designing simple UI elements to constructing complex, dynamic web applications, their expertise spans across a wide array of functionalities. A seasoned React Developer typically has a profound understanding of JavaScript and its nuances, including ES6+ syntax; they are adept at handling API integrations, state management, and even full-stack development with technologies such as Node.js. Furthermore, their experience often encompasses the use of libraries such as Redux or MobX for managing application state, and they are familiar with modern front-end build pipelines and tools such as Babel, Webpack, NPM, among others. Proficiency in performance testing frameworks such as Mocha or Jest is also a common trait of experienced React Developers. Hence, when evaluating the experience of a React Developer, it is crucial to consider their comprehensive skill set, project portfolio, and their proficiency in the diverse aspects of React development, including but not limited to, component lifecycle methods, hooks, JSX, and virtual DOM. These indicators collectively provide a more holistic perspective of their expertise and their ability to build scalable, robust, and efficient applications using React.

Absolutely, a portfolio of past projects is an invaluable tool when assessing a React developer's work quality; it is often considered a visual resume. This portfolio can provide insight into their skill level, creativity, and problem-solving abilities, crucial components for any React developer. A thorough portfolio should showcase a variety of projects, demonstrating the developer's ability to work within different industries and adhere to various design aesthetics and functionalities. It's also useful in highlighting their familiarity with the latest tools and technologies in the React ecosystem. Furthermore, examining a developer's portfolio gives you the opportunity to assess not just the final product, but also the evolution of a project from conception to completion; this can reveal their workflow, their ability to meet deadlines, and how they react to and overcome challenges. Thus, when exploring the realm of React developers or comparing options, it is highly recommended to review their portfolio to understand their capabilities better and make an informed decision.

Indeed, a React Developer's skill set often extends beyond the React framework; they typically possess knowledge of other technologies and frameworks imperative to project completion. The proficiency in these additional technologies is pivotal; as it not only broadens the developer's scope of work, but also enhances their ability to create more dynamic and complex applications. Among the common frameworks and technologies that a React Developer may be familiar with, are Node.js for backend development, Redux for state management, Jest for testing, and Webpack for module bundling and asset management. Additionally, a React developer's toolbox might include knowledge of databases like MongoDB or Firebase; proficiency in HTML, CSS, and JavaScript; and an understanding of RESTful APIs and GraphQL. These skill sets are integral in creating a seamless user interface and ensuring the application’s backend is robust and efficient. The depth of a React Developer's knowledge in these areas can significantly impact the quality and efficiency of the project, thus it is crucial to consider when comparing different React Developers. However, it's important to remember that the ideal blend of skills may vary depending on the specific needs of the project; therefore, one should focus on identifying a developer who aligns best with the project requirements. Understanding the diverse technological expertise a React Developer may possess can greatly assist individuals in making informed decisions when navigating the React Developers space.