Current accepted wisdom with Win 7 is to NOT use a cleaner.
If you ever think your Registry needs to be cleaned, repaired, boosted, tuned-up, cured, tweaked, fixed, or optimized it shouldn't.
In other words, injudicious use of "Registry cleaners" CAN & DOES cause problems.
IMO - there is no reliable way for a third party program to know whether any particular key is invalid, redundant or neither.
Some registry cleaners may not know for sure whether a key is still being used by Windows or what detrimental effects removing it may have.
This has led to examples of registry cleaners causing loss of functionality and/or system instability.
Should you decide to go ahead -
Make sure you have
1.a current System Restore point created.
2.a recent "Back up" of your computer- preferably to an external HD.