What it is?
Actually it’s nothing special. It’s a “Popper Stopper Locking Windscreen” (as reported on the package).
But as you can see from the pictures below, it seems David Gilmour has been using it during PULSE tour!
So I decided to try using the SM57 for the voice, and the results are excellent!
Anyway the A2WS sould be useful also when recording my guitar, to have a cleaner result!