ok, so I did this a couple of months ago.
Heat on my right heel?? Night and day difference. Was horrible, enough that I often had to ride with my foot off the peg, or with my heel on the peg and my toe facing outwards. Now, I can ride it as normal.
power? I didn't dyno it before and after, so I can't say for sure. And I haven't even had it over 11.5k yet. However, it seems to have slightly (but noticeably) brisker throttle response. Quite nice in my opinion. I know for certain that it didn't hurt power or torque.
Fuel economy? It has helped with this as well, if only a small amount. I can go 300km on a tank. Done it several times. Mixed driving types.
sound? Its a little louder, and a bit more "crisp" a bit more "snarly" nothing world changing, but a little bit.
The downside I find is that you can clearly smell exhaust now. Not just when cold, but all the time, when stopped, or if following the bike. Not horrible, but definitely something.
the fit is good, and it looks ok. Not amazing, but decent. However, the inside of the pipe shows a bit less attention. And yes, you won't see in there, but the exhaust has to flow in there. I don't have any pictures of it, but suffice it to say that it took me about 2 hours of grinding on the welds, and the excess metal. I have some fabrication experience, and decent professional tools, so I was able to do this. I don't have a flow bench to say how much was gained, but one of the joints was pretty poor tbh.
For the price I can't really complain, but I would like the inner surface to be smoother in something high performance. I've built many high performance cars and this pipe wouldn't be received with high praise.