Akrapovic does make a slip on. It'll likely cost double what the Yosh does and three times what the Hindle does. They'll all be RELATIVELY close for how they affect the bike's power output, with a little increase in exhaust flow meaning the bike will gain 2-4 hp, feel like it's breathing a little better, and a little better over-rev on top. Where you'll find the majority of the difference is in materials and build quality. Personally, I'd say Yosh is a good step up from Hindle, and Akrapovic from Yosh. Whether that offsets the price difference is entirely up to you.
Sound preference is a personal thing. The Hindle ss will be loudest, and higher pitched. Yosh has a deeper snortier sound, and Akrapovic is smoother. Akrapovic is a bit quieter at low rpm's and doesn't get really loud until you get it singing. Again, it's a personal thing which exhaust note you like best.
I recommend you find someone with those exhausts on a similar-displacement machine. Listen to them and inspect the quality up close yourself, then decide where you wanna spend your dough.
AND... there's a TON of previous discussion on this forum if you use the search button. Too much on this topic maybe...
