[Matty]

They don't "sound like a rotary" because they're hollow, they sound like that because the cam specs make the idle lumpy. The benefit of them is so you can pull out the lost motion assemblies and associated gubbins needed for VTEC, thereby reducing power loss and a little bit of weight. It basically turns your engine into a "regular" engine with super-lumpy cams, so to get the most out of them you really need to rev the bejebus out of them.