I really would forget about the registry cleaners. They are a waste of money and very often do more harm than good.
The "errors" found during a registry cleaning scan are not errors at all; rather they are usually broken file associations/other associations leftover from program installations that have now been uninstalled or changed.
You run the risk of corrupting the registry every time you run a registry cleaner.
The average Windows 7 Registry consumes about 125 MB of space, which is just 0.025% of an average 500 GB HDD, so the space saving argument is less than negligible.