I use the registry cleaner in CCleaner regularly and have never had a problem. As a matter of fact, after looking at what it wants to delete, I have always told it to go ahead without creating a backup and have never regretted it (you may choose to do otherwise and that’s fine). I therefore would say that it’s perfectly safe to use. When I uninstall something, I use CCleaner to do that too,then I run the registry cleaner (with no backup), then run Auslogics Registry Cleaner which sometimes finds additional left behind things. I also will sometimes use the older version 7 of Registry Mechanic which really does a thorough job and also has a registry compaction option. Auslogics and Registry Mechanic make automatic backups but I have never had to use one. I would not recommend any later versions of Registry Mechanic since it has become very bloated but the Auslogics offering is excellent.

The only Registry cleaning program I ever had a problem with was RegCure and it never caused a problem with the system. What it did was constantly delete valid things that would be automatically restored on the next bootup. I think they had it detect those things to make you think it was doing a better job than it’s competitors.