Pros - Deters night time predators, bob cats and coyotes.
Cons - Of course it doesn't work during the day...
For 3 years, I have been using Predator eyes on two pens that are located next to a gully, which I later found out, serves as an animal freeway! Coyotes and bob cats routinely travel the route. Since I put up the Nite Guard Predator Eyes, there have been no problems with them attempting entry into either pen. However, day time is another issue...but, all the chickens are locked up in their coops at night, all windows are covered with hardware cloth and bolted on, and the coop is surrounded by dig proof pens.
With all these measures it is still stressful for the chickens when they sense a predator outside. So Nite Guard Predator Lights/eyes are another good thing to add to the arsenal!
We already had a great horned owl problem. He visited regularly and knew what chicken tasted like. We than bought 4 of this product. It was properly installed. The owl still came 2 more times and killed two chickens. It did not work for us, but we already had a prior problem. We gave up and bought a guardian livestock dog.