Others may know better but I've never heard about cracked manifolds, only split turbo pipes. A few on here have had their cars remapped for more power without any problems.
They look nice yes, but im interested also what is the point of these. Cold air maybe but where does that air go. Or maybe its for the hot air that comes outWhat do these vents really do? I can't seem to understand the use of them? Looks nice, but when there is no need for them