Not sure if they make a great deal of difference over the standard DV in terms of performance (although they are obviously a bit stronger, and likely to hold boost a little better).
I fitted a dump-to-air on my old Coop and had a bit of a love/hate relationship with it...on the days when you wanted to blast it, the noise was great and added to the fun - on the days when you didn't, it could be quite irritating.
I thought that the recirc types still made a louder/better noise than the original part, but weren't quite so in-yer-face and irritating.