It's important to know that your content, intellectual property, and possibly confidential user data including full http request/responses are being proxied by this service. Their privacy policy is vague about what they will do with this information other than to say they will collect and process it:
"In running and maintaining our website we may collect and process the following data about you:
Information about your use of our site including details of your visits such as pages viewed and the resources that you access. Such information includes traffic data, location data and other communication data. Information provided voluntarily by you. For example, when you register for information or make a purchase. Information that you provide when you communicate with us by any means."