I can't speak for the e46 exclusively, but I have an e36 w/ the Dinan intake (engine bays are almost identical). I was very pleased w/ the performance gains from my intake. The intake roars under hard acceleration, and is so loud between shifts it almost sounds like a BOV.
As an added bonus, the engine bay looks very clean, without a large intake cone or heat shield where the air box used to be.
Hope this helps.