Be very careful with all Registry Cleaners and don't believe the hype which says things like "Frequent crashes will occur if you don't use a registry cleaner regularly" - - absolute rubbish.
I do use the one in Ccleaner, but I always check each entry it finds before clicking "Fix". More importantly, I maintain a drive image of my system at all times so if something screws up really bad I can easily recover from it.
And it's a myth that the registry needs cleaning anyway. Redundant entries won't do any harm at all, I'm just experienced and like to keep Windows as tidy as possible.
I don't recommend anyone uses a registry cleaner at all unless they have a proven recovery strategy in place,
but it's important to get the message across to "newbies" in particular that registry cleaning is not necessary.