I gotta agree with Jester here.. That exhaust fits the little Ninja perfectly IMO.
I looked it up online, seeing how much it'd cost to do the swap, and it's not much at all (like 60 bucks shipped, somewhere around there), but the exhaust doesn't look like a straight through at ALL! It has a resonation chamber before it changes angle, and I'm pretty sure it has some kind of stupid switch-back like the stock Ninja exhuast does. It's also a different mount, so you'd have to cut up your stock header/head pipe... Not cool if you ever wanted to swap to a different pipe, go back to stock, or even re-sale (I think people would look negatively on that, not being able to swap to something else themselves).
But, like I said, that pipes look fits the Ninja better than any other, even better than the HR-1 (which is a sick pipe, just way loud IMO).