Just thought I'd add my two cents.
My bike is a MY21/22 which in my country makes it the euro 5 compliant version I'm pretty sure.
I installed a CS Racing full exhaust last year, rode it for a couple of months (2000 or so kms) and then had the bike tuned.
Before getting the CS exhaust I was running the $8 mod simply to lose the weight of the factory can and so that I could hear the bike over the wind noise at freeway speeds (for some reason I need to hear the bike to ride properly..). Otherwise the $8 mod made no difference for me in terms of power of readability.
After installing the CS exhaust I noticed a pronounced difference in the bikes top end. It pulled longer, all the way to redline.
It also exacerbated the existing snatchy throttle issue that the factory exhaust had for me.
After I had it tuned (locally) it rode like a different bike. The peak power was more or less a wash, minor increase at best.
What this picture doesn't show is the significantly improved torque in the mid range at partial throttle and the complete deletion of snatchiness in the throttle.
This is nice on the day to day commute, but its a godsend on the track. Specifically on my local track which is short, tight and basically one long continuously changing corner. It makes keeping the bike stable at full lean extremely easy.
The TLDR is that, much like a slipon, the full exhaust itself is mostly going to net you weight savings and looks/sound. All the magic is in the tune. If you want more power but close to factory noise levels maybe consider removing your cat, doing the $8 mod and getting a tune (in person, mail ins are never going to be optimal).
Oh, forgot to mention. At 7-10K rpm it sounds freakin' awesome. I give it a blast every day on the way home from work and it still makes me giggle like an idiot every single time.
