I've had one on my FE450 '09 for a couple of months now and it adds heaps of smooth low end power which I really enjoy on technical hills and tight trails coming out of corners. I also have the Akra end-can (the old design) and together it's really good for a nice power boost across the range.
If I dare ask? How much does the header go for in US $? If there's one area of improvement I could see it would be the snap off bottom end at high elevation. 5000+ This is on a 2010 FE 450. The bike is perfect otherwise.