Try breaking one of these in normal use - I dare you! Mine has been sat on, dropped, soaked, carried between teeth (dog's, not mine) and still looks like new - and works!
My Working Cocker Spaniel responded to this instantly, and she was only a few months old. I don't work her and she only really gets basic training, but for a recall over big distances and in dense woods, this whistle is great.
I've found that quite a few other dogs pay attention when I use it, and even though they haven't been trained to it, they often sit in front of me or stand there waiting.
Best dog accessory ever!