Has anyone fitted a k&n filter and noticed any improvement ,panda 100hp

Putting on an air filter is not going to give a significant improvement in all honesty. In isolation it's a very minor mod. If you have loads of mods, then it becomes more important.

But, all said and done, do it for the sound alone.

I have one of these K&N fitted, i've not put my car on a rolling road yet to see if there is any BHP gain, but they sound great:

I decided to go for the k&n replacement panel filter. (partly because i like the black intake).
Found it seems to pick up slightly better out of sport mode. The best thing is however is my mpg has improved which tbh is a big grin for me lol................god i'm getting old.