The Cobra Sito pipe, which i have run, is from the leovince stock replacement line of exhausts. It is also a AV10 pipe, which means it will hit your center stand a bit, and drag on the ground, and you'll have to make a bracket to mount the back end. All in all, it's not better performing than stock and it does not fit the 50v well.
Have the folks at QC run one? Because you can take my word for it:
You may get some sweet air but you won't go faster.
The Doppler pipe won't do much for non kitted bikes. It's about the exhaust port timing, mostly. When you put a Doppler pipe together just don't use the restricted sleeve.