The pipercross kit was really easy to fit mate, it gives a nice roar in low revs and a nice tuned sound over 4000 revs. You will notice a better response nothing too breath taking but a definate improvement. Also would recomend a larger exhaust full system as the more air that comes into the engine the more air you need to expell through the exhaust. I had a K&N on my old punto and found it was extremely poot quality. It sounded nice but they have a nice shiney plate on the top with the logo and this fell off leaving it looking crappy, when i sent it back i got a replacement and guess what same happened again, also the rubber that connects it to the inlet pipe split and was seeping air. Pipercross is the way to go, If you have around £200 to spend go for a viper kit even better ive seen one on a mates punto, hardly any noise but air induction is much better. but as i said you would need a lrger exhaust with this kit for sure.
Sensible mods go far