Seems to me like it's the sort of thing that has some chance of working, but nobody can really prove it. Granted, I haven't seen many reviews of people saying they did get hit while using this product. Most of the deer whistles/horns I've seen advertised were much cheaper though, and didn't have an electric component. I think they were primarily wind-driven. The consensus however, seems to be that there is no consensus.
2012 Kawasaki Versys 650 - 20,500 miles
2000 Volvo V70XC 2.4T - 258,000 miles