itg improves the sound yea, not as much as an induction kit but saves the hassle of telling insurance as its just a new filter isnt it
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On paper an induction kit will give a power increase so I wouldn't try telling them it doesnt as they might be in the know.
I have had induction kits on a lot of my cars and never bothered telling them about it (aswell as exhausts) but then again I have never crashed and needed to claim.
Ring them up and say you are thinking of adding a modification to your car and see what they say.
imo i would get a refund on the k&n and go with a filter if the premium would go up but its your money and you can do what you want with it