Have 4 of them on my 4 runner, they are hidden in the grill area. I have always had them on all my cars and motorcycles, living in the midwest and traveling to the cabin they should almost be required. As they are noted they are called deer alerts, the high pitch noise causes the deer to look up to see what the noise is, so if driving at night you see their eye reflection and you are able to see them before they dart in front of you.
I like the term alerts because they just alert you to the deer, they will not make every deer run away, so you still need to pass with caution. I think that is were people think they "don't work" comes from, they will not make deer run away or keep them from always running out in front, but just like deer hunting, if you make a small whistle or noise to a deer, it will make them stop and look to see what the noise is. This pause and getting them to look is what you are after. And for only $5-$10 for a pair of them I need a lot more than an article to tell me they can't prove they work for me not to have them on my truck or motorcycle.