The Auslogics Registry Defragger looks good, but it's hard to tell if this or any Registry defragger or cleaner works. What's the challenge? Simple: It's not easy to gauge if these programs are effective because you'd need to benchmark your CPU against a range of programs before and after the Registry cleaning to properly test for any improvement, and that's an extremely time-intensive process.
Still, Auslogics is known for making effective Windows utilities, so perhaps we should give them the benefit of the doubt until more conclusive evidence is in. In any event, when you run the Registry Defragger, it spits out a report that you can review before proceeding with the potentially risky defrag process. The Registry optimization requires a reboot to defrag and compact the Registry.
This is a fairly serious program, and once you begin the analysis it won't let you move the mouse outside the program window. It also "strongly recommends" that users close all other programs while it runs, although this is a standard warning for Registry-cleaning apps. In our tests, benchmark improvements never materialized, but it's not impossible that there's something going on that we're missing. Recommended, but with a grain or four of salt.