I've owned this product since 2004 (I've upgraded it to the System TuneUp version since then). It does a very good job, but you have to really watch it sometimes.
It's been known to delete stuff from my registry and my PC that it considers temp or folders that aren't needed, but actually are necessary to some of my graphics software. I've had to re-install some programs after I used it to fix errors.
On the plus side, it does catch more than my Tune-Up Utilities. But, I feel more comfortable using Tune-Up, just because I don't want to weed through all the scan results Ace comes up with (just in case).
I mainly keep it as a backup for stuff that I know I really want to get rid of completely. Hope that helps!
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