Hi, I made an extened pipe that looks very much the same as the one on ebay, just not all that much chrome.
I used electrial conduit and put the stock muffler just below the rear wheel axle. I did not notice any change in anything, although I don't ever check for mileage, so I can't say on that.
It does'nt make it less noisey it just changes the direction and does make it a little nicer.
The only thing I would do in design change would be, the end of my stock muffler was about 2 to 3 inches from the rear part of the wheel, and as a result it spatters unburnt fuel and oil all over the rim and makes a big mess. I would just make the extention about 4" longer. And so if I was buying one like the one mentioned I would make sure "it" was long enough to omit this problem. Good luck.