yes bovs work
most turbo cars have a standard bov anyway, which vents back into the intake, so you dont hear it
when you upgrade your bov it will make no difference in performance if its a plumb back (plumbs air back into the intake as per standard) you may get a slight? performance increase
if you upgrade your bov to and external vernted bov, the car will run rich when changing gears and decelerating, also idleing can take awhile to stabilize after revving the engine, because the air flow meter cannot measure the missing air as the bov re-entry point on the air intake is AFTER the AFM, (the part where the bov vents it excess air back into the air intake) therefore making your car run richer, less air doesnt mean more fuel, the car is putting in the exact same amount of fuel into your engine, its just not getting all the air that the afm has detected in the air intake.
btw, i sold my legacy, i almost cried when i saw the guy driving it away, fuck that thing looked sexy, am pretty gutted now, went from a 15psi subaru legacy to a 2.6l mercedes nana car , o well my new rims arrive in a few days