Simon Grimm, a speaker and educator at Ionic Academy, discusses the versatility of Ionic apps in ensuring functionality across various platforms and screen sizes, emphasizing the importance of customization for both web and mobile applications. He highlights four key areas to focus on for enhancing Ionic apps: utilizing the responsive grid layout system, leveraging CSS media queries for adaptive user interfaces, checking platform compatibility to avoid unnecessary code execution, and implementing the Ionic Split Pane for a dynamic desktop UI. By integrating these components, developers can create apps that are both visually appealing and functionally robust on multiple devices. Grimm encourages developers to exploit Ionic's built-in features, while also suggesting that further customization through CSS can enhance the user experience, making Ionic a viable option for both native mobile apps and web applications.