I've had them on my Honda for years but haven't put them on my Harley yet, I have a friend who has them on his. I guess they work, never had a problem.
i have had them on all my bikes, here in northern ontario lots of deer, only hit one, minor damage to crash bar.after inspecting deer whistle i found that they were plugged with bug juice.so now i clean them regularly.
Used to have them on my Gold Wing years ago. Thankfully have never hit a deer on a two wheeler with or without them. I know you have to keep them free of bugs and debris. There is also a company that sells an electronic deer whistle. Its called (Hornet Electronic Deer Whistle). You can check out there website.