You will shift gears so fast that you will finish before you started. There could be some sort of time vortex created.
I would think it would be over kill since both do the same sort of thing in a different way.
There have been a PILE of issues with the quickshifter reported on here and I personally wouldn't touch one.
Here are a couple of examples.
http://www.google.ca/url?sa=t&rct=j&...paJLm33z5vrn8q
http://www.ft86club.com/forums/showthread.php?p=2257744