Cloudflare’s CDN service includes un-metered bandwidth for websites, subject to its acceptable use policies. However, user traffic is not always routed through the fastest or nearest data center by default. For optimized routing of dynamic content, Cloudflare offers Argo Smart Routing as a paid add-on. Argo analyzes real-time network conditions to route traffic along less congested and faster paths within Cloudflare’s global network, improving performance and reducing latency.

Argo is billed based on usage ($5 for first GB + $0.10/GB).

This is sadly part of the ‘free & unlimited bandwidth’ false marketing campaign. They tell you bandwidth is not metered, but they actually call it ‘Argo’. If you don’t purchase it, their CDN is slow and frequently mis-routes you through B-tier networks. - @rauchg