Is Clean my Mac reliable and effective?

It is reliable and effective in " BrickMyMac " function.

As the aka for " CleanMyMac " denotes, stay away form the Application or any other like Application.

Certain Applications maybe available on the Apple Apps Store and CleanMyMac is appearing - this only means the Developer is prepared to pay Apple a portion on each sale.

What the Application may do to the computer is up to the User to check this out before purchase

This will include CleanMyMac , 

MacKeeper

Dr Cleaner Pro Plus

Read some of the posting and arrive at your own conclusions.

Specific to CMM aha " BrickMyMac " 

After removing the offending Application as per the Developers Specific Instructions

Some Contributors suggest restarting in Recovery Mode and choosing to Reinstall the Operating System over  the existing installation. 

This may or may not replace elements of the Entire Operating System including the Home Folder ( User Account )  and replace any corrupted or removed elements of the Operating System and make thing right.

Then there are Other Contributors ( like myself ) would suggest  from this link Use Disk Utility to erase a Mac with Apple silicon.

For Intel based computer Use Disk Utility to erase an Intel-based Mac - Apple Support (CA) and then How to reinstall macOS - Apple Support (CA)

Thereafter to start from scratch and install all Required Application directly from the Apple Apps Store or Directly from the Developer.

If going this route - I suggest Not using Startup Assist to migrate things back as this will probably Re-Introduce the existing  issue that existed when the TM Backup was made 

No, this is not good software. It will slow down your Mac and it interferes with macOS security, making your Mac more prone to malware infections.

Don't use programs like clean my Mac, mac keeper etcetera

Never install any app that claims to "tune up", "speed up" or "clean up" your Mac. These apps exist for one reason: to separate the unwary and inexperienced user from their hard-earned money. At best they do very little, at worst, they can damage your OS installation and cause far more problems than they "solve".

Why do you think you need such an app?

What exactly do you think needs to be “cleaned?”

I haven’t “cleaned” a Mac in over thirty years, nor needed to. Neither have I had a need to optimize, protect, zap, or otherwise “maintain” any of the many Macs I’ve owned.

What problem are you trying to fix?

No.

(233163)

Junk.

If you install crap like CleanMyMac or similar, you will even get more scam messages.