A recirculation valve moves compressed air out of the intake tract when the throttle plate is closed and back into the intake, before the turbo, after the MAFS. The pro's are that you won't run rich when you shift, and your car won't backfire. The reason that happens is because with an atmospheric BOV, the MAFS is reading a set amount of air, and the ECU compensates for that amount of air with fuel. With that air not present, the car runs rich, and that is what causes the backfire. A recirc valve doesn't make a cool sound. Thats the only con.
A lot of people have gotten around this problem when using atmospheric BOV's by cutting their cold pipe (IC -> TB) and putting the MAFS in there, in that case, the MAFS is after the BOV.
EDIT: Or you could always switch to a MAP sensor
