I've used Puran's defrag. It does what it says on the tin and is one of several good free defraggers you can download. I didn't see anything in it that really set it apart from the rest. It did the job and didn't break anything doing it. That makes it good enough for me.
Their service manager looked nice, as did the shutdown manager. But I've already got those needs covered by other programs so I doubt I'd install them - except maybe
for a friend who wasn't too technical.
One big advantage you get with single function
utilities (as opposed to some of those all-in-one suites like Glary Utilities) is that a less sophisticated user has less opportunity to get into trouble since the app can
only do one thing.
As far as registry tools go, I have mixed feelings. Under Windows XP, registry fixers and cleaners could (in the hands of a knowledgeable user) yield some positive benefits - provided you didn't allow them to "automatically fix" whatever they found. Doing bare-bones fixes to the XP registry should be handled much like adjusting the truss rod in a guitar (i.e. gradually and slowly - with the absolute minimum done to get the desired result).
With Windows 7 however, I think registry utilities have the potential to cause far more problems than they'll solve. And with the changes Microsoft has made to how Windows 7 handles its registry, these utilities are now mostly useless at best IMHO.
Same goes for registry defraggers. I've never seen a case where defragging the registry did anything
, let alone improve overall Windows performance. So outside of possibly using them in some extremely rare service situations, I think they're also mostly useless.