I personally think Cloudflare is a terrible method of DDOS (any kind of attack really) prevention, they might of started off with that being their goal, but they veered of course when they realised their methods were actually quiet good at caching. Their security aspects of their service are laughable now, you are better off keeping those in house, with your own servers with dedicated (server) resources assigned to it.

If you use it just for it's caching, that fine, but I just laugh if anyone tries to convince me if it's good to prevent attacks on their servers.