I have always considered programs that make changes to the registry in order to improve performance a Pandora's Box. In other words, DON'T OPEN IT, DON'T USE IT! I must admit however, that I was tempted to click the "Optimize My PC" button for about .05 of a nanosecond (because this is avast! and they wouldn't steer me wrong, right?), but I did not.
So even though this is avast!, is it best to treat GrimeFighter like any other PC registry performance program and avoid it at all costs? Here's a screen capture of it and a link to avast! that explains what GrimeFighter does.