In the context of "should I use Cloudflare or Fastly as my edge", I lean Cloudflare. That said, I enjoyed listening to the GraphCDN crew choosing Fastly[1] – one crucial feather in the hat being cache invalidation[2] (miss ya, Phil Karlton) – and it sounds like a solid choice.
I've used both Cloudflare and Fastly for many years, and the cache invalidation at Fastly is a way bigger deal than people think. They're not competing for a 5% improvement in performance, they're competing with a totally different set of features which mean you can cache 80% more things, as long as you design for it. (Which I'm sure is why they don't aggressively compete on free plans -- if you try to just throw it in front like Cloudflare you won't see much of a difference from Cloudflare.)
With some careful design to take advantage of it, I've gotten 5-10x faster page loads using Fastly. (The last time I pointed this out, people accused me of being a sockpuppet account. Feel free to Google me!)
I can definitely see how new use cases opens up based on a 150ms (global) invalidation. Most of my use cases relies more on local invalidation and I haven't done enough homework about on what latency I really need (read: wrong line of business). That said; in the world of Cloudflare I think durable objects/kv store probably would come to serve as the next architecture for cache itself and lead to reductions in latency. Don't quote me on that though.
Yes. Caching is a different animal when you can count on fast, reliable, targeted invalidation. You can cache basically everything with super long TTLs, and just sniper-shot individual cache objects as soon as the backend updates.
Keep in mind that Fastly's C@E might not even be needed, as you get VCL as standard. You don't check pre-made boxes, you write a non-Turing complete but quite powerful language that gets atomically deployed to their whole CDN in a few seconds. I'm a big fan.
With some careful design to take advantage of it, I've gotten 5-10x faster page loads using Fastly. (The last time I pointed this out, people accused me of being a sockpuppet account. Feel free to Google me!)