freecycle.orgは安全ですか？

It is going to highly depend on who is running the local group. Your experiences are going to vary wildly. You also want to protect your private information and be wary of offline risks. Also, the site has broken encryption so I am lowering my rating one more notch. In theory things should get exchanged and less will end up in landfills. In practice ????

Generally a good site. No issues in using the website itself, so rated highly. But as with any social networking or selling site, you need to be very careful about how you allow people to interact with you in the 'real world'. Proceed with caution and meet in public places if possible. Don't give people your real name or address.