I installed the SP (Special Parts) Takegawa Sports Exhaust System today as a little performance mod. I went with it because it retains the same heat shield mount points as the factory exhaust so it's not very obvious and retains the bike's aesthetic.
Bought the exhaust from here -
https://japan.webike.net/products/24284332.html
Installation was easy following the steps in the official service manual (from Helm Inc) for removing the exhaust and then the instructions for installing the new Takegawa exhaust are in Japanese but they're pretty straightforward, all you really need to read are the numbers for parts showing you where they go, and torque specs in Nm.
My review is that it now sounds like a proper Honda with a fart can exhaust. As for performance, my seat-of-the-pants review is that it feels like it pulls a little better. I live in the mountains where this bike is generally as slow as an asthmatic donkey, and it still is, but it pulls up inclines a little better and on flat ground it feels like it has a bit more power in the top end.
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Takegawa exhaust on left, OEM exhaust on right
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Takegawa exhaust installed with heat shields off
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Rocky mountains from a parking spot of ~5,840 ft
Tools used were a metric hex bit set, 10mm socket, 12mm socket, Phillips screw driver, and a bicycle torque wrench
Other mods to the bike so far are KIJIMA Side Stand Wide Plate, KIJIMA Headlight guard, Barkbusters VPS on two-point mount (BHG-087), and Instacrate collapsible 46L crate on the rack. I have a ton of other parts to put on this bike, just slowly chipping away at it.
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Edit: Longterm review, this exhaust worked fine but did run hot and start to rust. I ended up replacing it with an Outex exhaust.