There's no need to actually delete the registry keys that PC Optimizer Pro finds, as 99.9% of the time, having invalid and needed registry keys, will not make a computer slow down, or actually cause any issues.
That is not entirely true. Obsolete reg entries can cause issues (then again might not), it is just not so obvious, since they are hidden, people usually "solve" it by reinstall. Like there was once an update for Windows 10, which failed to install, because of an obsolete reg entry, MS released an update, which was basically reg cleaner. People using reg cleaners installed that update just fine. Or someone failed to install a software for un unknown reason, it failed because there was a completely unrelated reg leftover from another software, once he used reg cleaner, he could install it just fine. The similar applied to leftover of AVs, drivers and so on and so on. I no longer recommend reg cleaners, since they are generally not welcomed, when someone post a problem, which I know could be easily fixed by reg cleaner, I just smirk thinking, I could tell you how to fix it, but will not, because I do not need to read dozens of comments claiming otherwise (like SSD vs HSS case, rofl), even though people using my advice solved the issue in about 75% of cases. Not like I care, what people think, I prefer facts and testing vs theories, but I just do not like arguing pointlessly about "believes".
To sum it up, reg cleaning, just like disk cleaning, does not necessarily solve problems, it prevents them in the first place. I did not start using it, because i was bored, but because of dozens of issues or annoyances, like with Windows Explorer or Windows itself. I am glad to be running completely problem free computers for years, using deep reg cleaning. Of course, that applies to reliable reg cleaners only, not to regseeker or similar. A bad software (promoted by search engines on top) gives a bad name to good ones, understandably causing all this aversion to them.