If your Mac is slow ..... you'd be much better off removing unused language packs, duplicate files, and all residual files from previously uninstalled software(s)..... and use the Disk Utility to repair your disk permissions ...
MacKeeper is one of the best third party utilities to help keep your Mac optimally tuned and running well.
I have tried
Clean My Mac and other similar offerings, and they do not do anywhere near the job that MacKeeper does ...