No they don't work. About the only thing you can do with roos is avoid them. Choose your riding times and locations - and speed. Even the Shu-Roo things don't work 100% of the time. It is one thing to scare a roo off the road, but it usually isn't the ones ON the road that you'll hit. The danger is when they come on to the road from the side. The only way to avoid those buggers is to be travelling slowly enough to brake.
Just my experience.
Work to live, Live to Ride!