Trixie High Frequency Dog Whistle - With Frequency Protection

I bought this and it worked for about a week and then the whistle stopped no matter how much I took it apart and tried to repair it. A complete waste of money, I shall now spend out on a decent one which I should have done in the first place.

I bought this as we used dog whistles in our training class. The ones I used in class could be heard where as this one is an almost silent whispery noise. I'm not sure if only dogs can here it? I tested it out by getting my dog to stay behind a wall and then blew it three times and he came but I wonder how well this works outside on a windy field? I'd be interested in hearing if anyone has had success with it? I gave it a middle star rating as I'm not sure how confident I am that it works, I prefure the ones I can hear too!

Not strong enough