Is kms/activator safe?

Have a license of ms office, but dont want to use it as it keeps on updating in the background plus don't want to sign in using the linked email. No updates are needed in office products unless one is using a cloud service like 365. Now the question is if ms office iso is downloaded and then kms is used or suggest a better activator, then will windows auto update it? Does kms or activator mess up something which is not good for registry etc.?