Registry cleaners market themselves as tools capable of removing redundant keys and invalid entries. Microsoft does not support the use of registry cleaners. Registry cleaner PUPs are usually installed onto systems via manual download from websites. It is best for users to do their own research first and/or ask around in software and security forums to get answers. Registry cleaners are usually free to download and install from trusted sites such as trusted sites. They can be harmful to systems, spyware, adware, or worse, malware.”]
Source: https://blog.malwarebytes.com/threats/registry-cleaner/