The pricing model on this makes no sense. Argo claims to optimize the route between Cloudflare and the origin, which is only used during cache misses, yet they charge $0.10/gb for all traffic from Cloudflare to visitors.
Considering most sites will be aiming for a high cache hit rate, I don't see this being very attractive unless your user base is constantly logged in and hitting your backend.
Not all content can be cached,that's where optimal routing to origin provides the most benefit...for instance if you're serving pages with PII after the user logs in, you can't cache that on a CDN (you can do browser based private caching though).
Considering most sites will be aiming for a high cache hit rate, I don't see this being very attractive unless your user base is constantly logged in and hitting your backend.