CBR's muffler is a flame-friendly topic...in my opinion.
The aftermarket ones I have seen so far don't improve significantly how the bike's looking, so I would prefer keeping the original (matter of warranty, matter of taste).
But it's to be considered that "look" and "sound" is not the only aspect: what about specs?
Did you find improvements in top speed or torque or whatever?
How do you feel the bike? Different?
Top of all: how do you feel your wallet?!