CleanMyMac X often gets confused with shady things like MacKeeper, but MacPaw, the Ukrainian company behind CleanMyMac X is highly reputable. I’ve worked with several individuals there over the years and met them at conferences—they’re legitimate.
MacPaw also created Setapp, which provides access to many Mac apps for a single monthly fee. The fact that a wide range of Mac developers work with them (and have for years) is another indication that they’re not some fly-by-night company.