Graham Goode give instruction for fitting an atmospheric dump valve, I fitted the GGR one it cost me £150 for the valve and another £70 for the take off pipe.
My FRS does stall occasionaly on dipping the clutch at junctions but the GGR instruction tells you to raise the idle speed by adjusting the throttle idle adjuster screw. This will invalidate your Ford warrenty but if you want to avoid stalling it's what you have to do. Having said that it doesn't happen to all cars, it's different in every car. I havn't adjusted mine yet but I'm still undecided as to stay with atmospheric or go back to recirc.

What gives the best performance? Can you notice?

K