Sorry tractorman, in reply to your question, the only benefit that i ever heard of is that a release to atmosphere dump valve was supposed to help spool up and throttle response and prevent turbo stalll... but i cant see how it would do any more or better than standard recirc valve.. imo its all for the sound, thats the different,,,,,...
well thats unless your running mad power and standard recirc valve mite not be deemed good enough to hold back big 2bar and over boost levels, fmic will force you to use some form of aftermarket dumpvalve wheter it be recirc or atmopheric... hope that sheds bit of light for you