When I lived in eastern Oklahoma there were 3 instances where deer came in contact with my truck (2 in one night within 2 miles of each other). I had the deer whistles on my truck every time. As soon as I took the dern things off I had no more issues. I very much believe that deer whistles are worthless.
I have a brother-in-law that used to ALWAYS have deer whistles. He kept hitting cows.
As for me, I've driven since I was 14 (64 now). Everything from motorcycles to 18-wheelers. In 50 years of driving, I've hit one dog, and that is because he was a car chaser. (Knocking on wood.)