Note that:-

• The “before cleaning score” is the score when some heavy games and apps running in the background 
• After testing an app we restarted the phone and the test is repeated with another app

So finally, does clean master actually work?

So our result shows that there is some improvement in scores, but actually, an inbuilt task killer feature does the same thing. And this feature can be found in all Modern Android devices.
Almost all apps run a background service for a better experience and this background service can’t be killed by the clean master.
When you launch an app that app runs on RAM. and Clean master clear this app from the RAM but the background services of the app still running in the background.
So the simple thing is that many new Android users don’t know much about it. They love their phone so they search for a phone booster or junk cleaner app on play store. The first result is always Clean master and that 1 Billion download mark attracts like a magnet.
The Junk Cleaner is actually a Cache Cleaner and You can clear cache on Settings-> Storage-> Clear Cache.
And let talk about the Antivirus feature. So I am using my Android device for last 2 year and I never installed any Antivirus app. And the result is that I never got any virus on my smartphone.
There are some websites online which sometimes gives a Notification about Virus on your Device and Redirect you to Play store or gives you an apk file to Download.
If you Downloading a file from a website then there some chances that the app is a malware. They just display some advertisement on your Android screen. They can be easily removed by hitting the Uninstall button of the app. You don’t need a separate app for removing an app.
Android’s RAM management and cache management system are good already and you don’t need a separate app to clear cache or clearing RAM.

How Android handles RAM

How to stop all heavy apps from running in the background? (for real!)