I've seen it before but I've never seen anyone use it, for that I'm thankful for.
Saying that, I have seen a clear plastic cup placed on a cockatoo's head so that the cockatoo would not bite the person doing a routine exam or otherwise on the cockatoo. Mind you, this was a 40+ year old cockatoo that was taught to take vaccines into the breast force-free. This 'too would sit on his perch while someone could go up to him, reward him, stick a needle into him while continuing to be rewarded, plunge the syringe and then be able to remove it.... without having to physically touch the 'too, let alone restrain him.
The plastic cup was an added "safety" measure, not that the 'too was likely to bite anyone anyway! When he saw the cup he "assumed the position" for the cup to be placed on his head and would lick away at the cup, completely ignoring the needle and syringe! Once the procedure was over with, the cup was removed. He generally enjoys having the cup placed on his head, so he doesn't view it as a negative experience!