Stage One flash simply returns your bike to the same lean condition it had when it was new. A fuel tuner will cool your bike down and give you a small boost in power. The TFI from Dobeck is a great, simple tuner and you get a forum discount, too. If you want something that allows you to tinker more with the settings, there's several other good options. Just let us know which way you're leaning and you'll get lots of help and input.
How can the engine run lean if it has an o2 sensor on it?