I also had to go to EWG on my 11' WRX because of boost creep. It solved the problem instantly. I was already using a EBCS and just added the EWG. I choose a 38mm. Anytime the EWG is open ~15psi+ it flutters. If you dont want the flutter you can choose a MBC. At one time I disconnected my EBCS and ran it on WG spring pressure and it was a smooth constant dump. The flutter doesnt bother be but its not for everyone.
Make sure you get with your tuner on what spring to run. Im running about .1bar to light but I experience almost NO taper.
Make full boost (19.5psi) @2700rpm also =D (VF52)