As taken from the R&B website:
"This manifold removes the restrictive elbow, and due to it's unique design, it has been flow tested and at 2 bar of boost there is only a 2% disparity accross the cylinders. This is considerably better than the OE manifold."
Proof that a tapered swedish plenum can work well.
Mikes tapered swedish plenum design has been run on successfully on many big power cars.