I am not to sure about duplex, but I sure as hell know that brasso works, and pretty well I might add. It is great for the hairline scratches and a bit deeper than hairline, but the ones that you can feel when you slide your finger nail through would still be there, but thats with any material. The problem with using brasso though is you have to use it for at least 20 minutes to get rid of a spot of scratches.
This is how I do it;
apply brasso using toilet paper on one area
wait ten minutes
use an old cotton shirt to wipe for 20 minutes
ten minutes in put brasso on another spot
once the 20 minutes is up start brassoing the other spot
repeat
this would help your macbook look good as new, and it looks more "polished" if its an older laptop, makes it look like you just took it out of the box
of course now I have a new 2.4 penryn blackbook with an incase hardshell on, so that isn't an issue for me anymore