I fitted one and have run it for 6 months you will notice the differance through the mid range power.
I am now thinking of going for a new Garret roller bearing turbo which will require a new manifold, so if you are interested in a second hand ceramic coated Primary Designs manifold for the focus rs give me a bell.

A new one will cost you about £1300 with coating.

Make me an offer for mine.

K