Love CleanMyMac! It's easy, clean and does what it says. Very trustworthy software. Had no troubles at all. I recommend it to my family and friends who use MAC OS.
It is good that you can first try how sensitive the program is in finding unnecessary files that slow down your computer. And only if you are satisfied with the scan results you are welcome to purchase it.
Very good at detecting detritus after uninstalling apps, can be a little annoying when updating another app.