Indeed Sam, that's what I think too. The surge back shouldn't happen in the first place as it could damage the charger, even if it's in the long run. And considering that the Rotrex is sold as a sealed unit, it's even more important to avoid any surge back.
One of the authorised sellers for Rotrex, TTS, said that once the sealed unit is damaged or opened, they get scrapped and replaced.
FYI, the BOV in above vid is open during idle and when the engine revs, it starts to close and is fully shut on wide open throttle.