No Apple or other tech I know will advise you install such things.
As to keep you iMac secure you usually can do this by never installing such because it's usually spyware or has other goals like showing you advertising.
As to "clean", I've had Apples for a decade. Never found then to get cluttered outside my own files.
I had MacKeeper on my iMac, suddenly it's gone and something called Mac Tonic is in it's place and wanting me to pay for it. I'm thinking MacKeeper changed to Mac Tonic, I searched for Mac Keeper and a discussion on Apple Inc said do not install MacKeeper because it's nothing more than malware. Is this true? What about Mac Tonic? Are both these malware? Can anyone suggest a program to keep my iMac clean and secure?