What people experience after the use of registry cleaners are random. I do use registry cleaners but in a very controlled manner. I remove those things that I know are from the programs that I know are gone but those that are really weird, I tend to leave them alone.
You are really lucky if you don't get any problems, get performance gain and remove malware remnants after the use of registry cleaners. But those that have bad experiences with them will stay away from them. I say, reserve a backup, a restore point or a complete registry backup using Erunt.
Th authors of many registry cleaners would do anything in their power to make their software looks so good and superior to others in their websites so you'll be tempted to buy them and give them money. Those brands are not designed for inexperienced users. Its business, basically.
The makers or CCleaner are however, in the humble pack. At least they don't brag about these falsified software reviews and all of their products are free. CCleaner is also not an aggressive one, unlike others that can cause a lot of harm by removing too much. I love CCleaner.
Threads like this tend to create more and more debates about the efficiency of registry cleaners. That happened dozens and dozens of time on this forum. But opinions will remain split.