Isn't it easier to just use Charles Proxy (http://www.charlesproxy.com/) or mitmproxy (http://mitmproxy.org/) for those stunts? I can see the value for anyone not familiar with those tools, but for me as a developer, this is clearly something that can be solved without depending on a third party server.

Sometimes you need to do it from a device that can't connect to your local network.

Nope. It will proxy everything you ask for.