They have a nice advertizement that promises a lot

But only delivers on those parts that are already integrated in OS X. The most glaring inadequacy is .RAR files which are not recognized 9 out of 10 times. even 7z files are rarely processed. Finally, their .sit files are almost never seen in the wild. Thus this software is not needed since many of the functions don’t work anyway. It used to be quite good but has really went quickly downhill since 2011. Now it doesn’t seem to be supported… Why doesn’t Apple remove apps like this!

Wizbang Trainer about StuffIt Expander