The scene in question:
To be honest, I have not seen a flash bang in real life. After watching some demostrations it wasn't hard to believe that what Batman used was a similar device with a little movie flavor. As how Bane was "impervious", well I didn't mean that it wouldn't have blinded him momentarily (from my understanding it's a matter of seconds). But Bane did see him in the darkness later, that's what I meant that it didn't matter if they blinded him or not.
So flash bang or not, as for the reasons, I think Anno got it more or less right so I wouldn't delve further.