Have any of you hunting guys ever used "sound amplifiers"

I am not a hunter, but I like walking back in my woods
and just listening to nature...last Thurs I was back
there and was surprised to find a large hog was actually
wandering around so close to me as I was sitting on a log.

Any of you that have used sound amplifiers
do you have any suggestions on a good one?
Do these things work?

Hunting Sound Amplifiers @ Bass Pro Shops




Fishing has never been about the fish....