While I think they are right that registry cleaners don't give you a speed boost and those claims are false, sometimes they can help cure little software or Windows related problems, or software that won't install/uninstall properly. But if there's nothing wrong with your computer in the first place, they will do nothing useful. I would agree CCleaner is the least aggressive and therefore the safest to use, I've also used Glary and Auslogics over the years.Â
But you certainly don't need a paid registry cleaner thrust upon you when you boot your computer, and it probably got there through somebody else's installer. Those are the ones that are being targeted.