I don't know about things being kosher or not, but I used to have the same sort of opinion about Clean my mac.app but I have been using it occasionally over the last several months and I must admit I'm quite impressed, but the user must have a rough idea of what they are doing.
Neither does the Application hold the user to ransom as some other cleanup programs have a nasty habit of doing.
I will say that I was quite impressed when CleanMyMac 3.app cleaned up a small problem that Onyx wouldn't and also Trashed some old files that provided some extra free space on my hard drive.
I don't know why so many seem to give it such a bad reputation and tend to group it in with applications like MacKeeper.app etc. I for one find it to be quite useful as do some sites who recommend using it.
Just saying... I now keep it as one of my Mac maintenance tools and use it occasionally and find it works quite well.
EDIT:
PS: I have not used the latest version of CleanMyMac X 4.6.3 that requires OS X 10.10.0 or later and I believe it's price went up a bit from the older version.
CleanMyMac X for Mac. Download Free and Review [Latest Version] macOS
Good gosh Patrick, wash your mouth out with soap! Just kidding
I think if you do a search on this forum you will find that I have defended CMM almost every time it has been mentioned. I have been using the app since inception, years ago and although I agree that it could potentially do harm it is a tool like any other and requires the user to understand what they are about to do before giving it permission to run, especially some of the optional scripts like "Free Up Purgeable Space". I maintain you could cause similar problems with OnyX if you change default settings or even Daisy Disk or Find any File if you delete files from the UI without understanding the implications.
Both my wife and I use Clean My Mac X and she simply runs the Smart Scan and Clean with never a problem. We have both trashed hundreds, probably thousands of gigabytes of unneeded data over the years.
Others will argue that everything it does can be done manually and of course they are right but I'd like to see them do it while making a cup of coffee and in the same time.