No, it is not safe to use registry cleaners to speed up your PC. Registry cleaners work by scanning your PC for certain errors and problems and then attempting to fix these issues. However, registry cleaners are not entirely reliable and there is a chance that the cleaner could cause more harm than good, such as corrupting important registry keys which can in turn cause major instability or even crash your system. Therefore, it is best to avoid registry cleaners if you want to maintain a healthy and stable system.