Mk2 Focus RS Breathes more easily with this and the RS500 airbox. Noticeable increase in breath-ability and suction sound! It seems to go faster but it could be in the head. Definitely worth it. If you compare the OE setup to the Mountune one you can see that there is greater breathing capacity in the Mountune one by at least 33% - i.e. the connections are just bigger/wider.
Easy to install and makes nice sounds
Great product and excellent value. Easy to fit and high quality. Would recommend.