As to deer whistles, I think that I saw a test on TV concerning them, and they didn't seem to affect the deer in any measurable way. They might or might not hear it - or if they hear them, they may not associate the sound with danger, and continue to do whatever it is that they are going to do.
When I am in the woods hunting, I can hear a car traveling on a paved road a quarter mile away. On a dirt road, sometimes further. Deer can hear much better than I can and I don't think that they need whistles to know that there is something there - they just don't associate the car with danger, and/or cannot determine how far away/how fast the car (or bike) is traveling.
But, the whistles make some people feel safer, and it stimulates the economy. I guess that amounts to something.