I have an 08 with a Two Bros S/O and it has a nice sound to it. Not real loud, but if you jump on it, it sounds great. I also just gutted the header cat and it is a little louder, but has a nice deep growl to it. It's pretty simple to install, you might want an assistant there to give you a hand if needed. The hardest thing about the install was removing the EXUP cables from the stock exhaust, and that took all of about 10 min to do that.
Here is a youtube video clip of an 09 with a Two Bros.
[ame=http://www.youtube.com/watch?v=mF0zQNlG620]YouTube - 2009 FZ1 with Two Brothers installed[/ame]