I worked with Something New on rebuilding Oscar's marketing site. I helped with deciding architecture, building components and page templates, and setting up data models/integrating with a headless CMS.
The site is essentially a single page app built using React/Redux. There were originally some mini interactive elements/data visualizations built using Pixi.js. The content is managed through a headless CMS.
Using a single page app for a marketing site had some pros and cons. The pros: seamless transitions, re-usable UI components, being able to host the entire site statically on a CDN. The cons: the added complexity that comes from single page apps - build setup, state management, etc. Also extra work is needed to make sure things are optimized for SEO, which is generally important for marketing sites.