Well this is probably going to be controversial, but here's a quote from a global moderator at Bleeping Computer:
"Why you should not use Registry Cleaners and Optimization Tools
There are numerous programs which purport to improve system performance, make repairs and tune up a computer. Many of them include such features as a registry cleaner, registry optimizer, disk optimizer, etc. Some of these programs even incorporate optimization and registry cleaning features alongside anti-malware capabilities. These registry cleaners and optimizers claim to speed up your computer by finding and removing orphaned and corrupt registry entries that are responsible for slowing down system performance. There is no statistical evidence to back such claims. Advertisements to do so are borderline scams intended to goad users into using an unnecessary and potential dangerous product.
Credit for this goes to Quietman7, one of the Bleeping Computer Global Moderators."
I've seen similar posts in other forums and personally I concur, FWIW.