is a k and n filter worth buying, any noticeable difference ?

[SpiceWeasel]

I fitted one to my bike many years ago, I think it makes a little bit of a difference. I seem to recall reading the FZS run a bit rich as standard and the extra air flow helps a little bit with fuelling. If nothing else it gained a nice howl from the exhaust near the top end.... I just have a Venom race can fitted.