AFAIK, this is the only Mac app out there that can decompress 7z files, so...if you need it, you need it. I'm just glad I don't need it very often.
It has virtually no GUI. I drag a z7 file to it, and the only way I know it's working is that my system slows to a pathetic crawl. No progress bar, no file list, no indication of any sort that it's doing anything. I fired up Activity Monitor to see that it spawned another process to do the decoding, and that process was hogging virtually all my CPU time, to the point where it took several seconds just for clicks to register. NASTY.
So, it gets the job done. It doesn't do it really nicely, but I'm still glad to have it.