CloudFlare is a proxy that just happens to use a CDN for some things, it's not really a CDN otherwise. And really, unless your host is bad, it's not worth using unless you have a ton of traffic and have security concerns.
Let me clarify.
First of all, they don't consolidate your css and js files because of namespacing issues, but having that as the ONLY option is utter nonsense -- all my js and css have no namespacing issues, so where the hell is my option to reduce http requests? Dumb.
Secondly, their 'rocket' service is crap. It screws up 50% of the js files existing on your site, including even some non-js files. It's terrible unless you build your site from the ground-up to work with it (which would be silly).
Thirdly, having them cache all the standard jquery and bootstrap and other things that google sites hosts is absolutely attrocious because 90% of the internet already have the URIs cached from google anyway. They even admit this lol.
Fourthly, if your site is low traffic, it takes a week for them to even cache anything. This means if you make any changes you have to purge the file and wait another week. What? Retarded.
Oh yea and lastly it has issues with random ISPs and will scare off potential clients if you're a product/service site, so turn off security enhancements completely unless you're knowledgeable in this are and need it for a specific reason.
I *suppose* it's brilliant in theory, but in practice I personally think it blows donkey balls. Wait for Google's version of this and CloudFlare will be gone with the wind.