Do the more expert Mac users in HN recommend it?
MacKeeper is indeed shady, but I think Clean My Mac is a great piece of software.
I could swear I've seen those "Your Mac is having a problem" ads that fake being a system error trying to get me into Clean My Mac 3, but may be it was MacKeeper.
The uninstaller is very convenient for me and I use it often, as it tries to detect configuration files and asks to remove them as well.
MacPaw is actually quite respected as a developer. Enough so other developers trust them to steward the "Netflix for apps" Setapp.
More stuff I install with brew-cask on my macs: https://github.com/andreis/cfg/blob/master/brew-cask.txt
When you upgrade from one Mac to another, you can use "Migration Assistant" to get all your apps, docs, and settings on the new Mac. This _also_ brings across all the leftover cruft from apps you no longer use, but whose data is still in your ~/Library folder (hidden, contains the working data for most apps)
Repeat a couple of times, and your current Mac will have large amounts of files that are leftover from your current mac, your previous Mac, _and_ even from your earlier Mac!
"Clean My Mac" will help remove this accumulated cruft.
Source: Mac developer whose product is guilty of using ~/Library to store a large database.