Taking the CNN front page for example. If you set a TTL of 60 seconds, and you have 14 edge locations (taken from the CloudFlare about page), you've got to satisfy 1440 * 14 = 20160 requests a day. The CNN page is currently 97527 bytes, which gzips down to 20,346 bytes. That's 391 megabytes per day. Serving the edge locations even with this relatively short TTL is trivial.
Now, the TCP connection means the content can be pushed and not pulled, so latency is better. It also means that caching a lot of pages will become cheaper (though still expensive).
But it doesn't seem like a lot of benefit for essentially replacing HTTP (between the content servers and the edge nodes), for all the proprietary software and vendor lockin that entails. For each byte you're sending to edge nodes, it's going to be served up orders of magnitude more from the edge nodes to end users, which seems like where almost all the cost would lay.
I'm sure they know what they're doing, and that their customers have asked for this, but think some real world case studies would help make it click. That the blog post is going on about 'caching the uncacheable' really doesn't help.