Most of the world's whistles have the labium on the back - I'm just back from a couple of weeks playing Moldavian Csango music, and their whistles are a lot easier to play outdoors than a British-type one. They work fine with a mike, you play with the instrument side-on to it. Chinese whistles are made the same way.

There's no beak on a Moldavian or Chinese whistle - the top end is cut off flat. This allows for a vibrato achieved by shaking the whistle longitudinally against your lips. I don't know quite why this works, but it does, and you can't do it with a Generation or the like.