I first purchased 3 several years ago and they worked except that then, I lived in the city and there were lots of lights & the opossums were not deterred by them; in the city, they are used to lots of blinking lights. I gave those 3 Nite Gurad lites to a friend because he was having trouble with coyotes (in the country). He reported he had not seen a coyote since putting the Nite Guard lites out.
I purchased 4 new ones when I moved to the country and installed them in strategic directions about the perimeter of the chicken area. I walked around the property at night and took in consideration the grade of the land and the directions predators would be coming from. I moved them a couple of times after walking around at night & observing from where and how they could be seen/observed. So far, no predators, except a lone opossum, but I also have a good dog too. There are coyotes and fox all around me. Deer are moving and people are feeding them around me, but they also will not come on my property. I was told before I moved here to expect deer right up in the yard. Whether it is the Nite Guard lights or the dog OR the combination of them both, I can't say, but nothing comes in (my dog killed the opossum that came in the yard so I guess my lights are warning of a real threat).
When I purchased the first three lites, they were about $8 cheaper a piece.