my $.02
We have a few of these placed off of the dock down at LOZ. They work GREAT!!!!!!
My only complaint is, they are a little pricey. The pvc part is easy, I can get just about as much as I want from work for free. However paying 30-40 bucks for the balls is a little ridiculous.
My future in laws who own the place continue to sink them around their dock and they continue to produce!
We have also begun sinking the cheaper PVC structures as well, simply using concrete a dishpan and scrap pvc of all shapes and sizes.....total cost of one of those is around $3 a piece!
But to answer your question, THEY WORK!!!!!!! on LOZ at least!