That's certainly nice .
I'm not sure in what degree it affects the battery performance but it certainly wages in .
Maybe some user can shine some light on this.
That's pretty incredible when you look at the JavaScript speed tests between safari with the nitro boost vs google chrome without it. The difference is milliseconds. You can run these tests yourself too. Just google SunSpider JavaScript benchmark or something like that and you'll get the link for all the different JavaScript tests you can run. We're talking very small time differences.
Regardless, its a tweak I purchased on launch day and always keep it installed. It does have its advantages. I have noticed no battery life impact. You can try using your phone with and without it. I bet you get the same (or very close) battery life.