There's the option for free plans: Basic DDOS protection with the following blurb:
Built-in security measures automatically protect your website against DDoS attacks. CloudFlare's service allows your legitimate traffic to reach your website, while stopping illegitimate traffic at the edge, before it hits your server.
So Cloudflare promises least a minimal protection for free plans.
As for Siege, I assume Cloudflare is optimized to protect from botnets. A single machine running Siege is not a realistic test case. Perhaps it also depends whether your website is mostly static, then Cloudflare can do a lot of caching.
Built-in security measures automatically protect your website against DDoS attacks. CloudFlare's service allows your legitimate traffic to reach your website, while stopping illegitimate traffic at the edge, before it hits your server.
So Cloudflare promises least a minimal protection for free plans.
As for Siege, I assume Cloudflare is optimized to protect from botnets. A single machine running Siege is not a realistic test case. Perhaps it also depends whether your website is mostly static, then Cloudflare can do a lot of caching.