Other addons already do this? Rated 3 out of 5 stars

Is there anything that this addon does that cannot be done by, eg, RequestPolicy?

This review is for a previous version of the add-on (0.3). 

Sorry, dont know much about RequestPolicy. I think RequestPolicy is a good addon. I've just tried it. When i visit my blog(http://hi.baidu.com/yarcowang , sorry it is Chinese) with RequestPolicy, something get lost even after i add bdimg.com to the whitelist.
(Maybe something different in internal, otherwise you can treat SFW as a simple method instead of RequestPolicy if you dont need a lot of options)