I use them and swear by them. I had a predator problem before I even had chickens: raccoons kept getting my Koi and goldfish. Even when the fish were gone, the 'coons would still ravish the pond plants looking for more fish. Nightly. So, when I got chickens and built the run, I made sure it was very secure. Then I saw the Nite Guard lights, and bought some, setting them up on three sides of the chicken run. (The fourth side was within a few feet of the house I rented, so I imagined predators wouldn't come from that direction.) Anyway, the raccoon predation stopped just like that. The ponds were "outside" the Nite Guard perimeter, but there were still no further attacks on the ponds. Or any on the chickens. Well, once a very young opossum snuck into a coop during the day, to sleep, when the lights weren't operating.
I have since moved to a much more rural area and brought those Nite Guard units with me, setting them up here. No problems with night-time predators in the coverage area. (Two ducklings wandered away from the coverage area and were killed, and a pullet stayed out all night and jumped down into the unprotected gully, and she was killed and eaten, so I know there are predators around. But they haven't breached the coverage area.)
I plan on buying some more and expanding the coverage area.