I've just fitted a pair of Akropovic pipes & Kev's O2 mod and can quite honestly say I'm pretty over the moon with the results.
They work really well together power delivery is much stronger , cleaner & smoother from lower rev's than before. No horrible shuddering low down now. I have got the fuel mod as well but not fitted yet I'm only thinking of fitting it later if I change the standard air filter to DNA. I did remove the snorkel up until it's first service then put it back in, mainly because I intend to ride a few dirt roads and found that after the last hose down water can get under the seat and lay in the bottom of the exposed filter. Which leads me back to the exhaust fitting. Akropovic supply a heat sheild replacement with the pipes that fixes in place where the mounting bracket go. But looking at it on the initial first fit it leaves big gaps in the rear under guard assembly which would allow water & mud to spray up from the rear wheel & find it way onto all the electrics behind the battery. So have used all the original parts instead which seal things of nicely. I'm thinking the most rearward heat guard has changed slightly on a 11/12 model as the photo instructions included show things a bit differently.
The noise level of the cans isn't much louder than standard but a nicer note, the decibel killer inserts are still in as I often find my self coming or going to work between 1am- 4am so keeps the Neighbours happy. I'll give them a go one day though without the inserts to see what they are like.
Just also say a big thanks to Kev for finishing off properly what Yamaha started great work mate, & hope your enjoying the new MT