I’ve used TweakNow Registry Cleaner before and now using Registry Mechanic and I don’t have any problem with both of them. I don’t think it will caused you any problem as long you know how to used it. Futhermore there’s backup tool to do some backup if you accidentally delete some unneccessary keys. And there are option in both registry cleaner whether you want to delete or just let it be there. So if you not sure you can skipped the keys. And sometime it’s very helpfull when you’ve face virus problem.