is it safe to use a registry cleaner?

Registry cleaners can often do more harm than any minor good---even to the point of making your computer inoperative--- especially if you are not well-versed in computers and their operating systems, and have games and a lot of applications on your hard drive.
You can get more "bang for the buck" by using Windows Cleanup, manually reviewing your applications and files for those you don't need and deleting them, running checkdisk (scandisk) and then defragging your hard drive (the latter two steps on a regular basis).

no as long if you find the right one