I bought this to help protect my allotment from browsers, chiefly rabbits I suspect. Since I installed it areas within its radius of effect have definitely been avoided by nuisance animals, only otherwise unprotected plants outside of this radius have been nibbled.
Additionally, it appears to be very economical with batteries. It takes 2 x 9v batteries, and the first pair of batteries are still going strong, several weeks after installation. This contrasts with my other ultrasonic pest-scarer, sold at a well known DIY store as a dog and cat scarer; also effective against other animals, but it eats AA batteries for breakfast, and may prove too expensive to maintain to be worth it. If I have to ditch that item, I would be more than happy to consider buying a second Strikeback repeller to replace it, they are equally effective and the Strikeback seems far more economical to run.
So: it's a tad pricey to purchase, but running costs are so far minimal and it does work to deter the bunnies; so can recommend wholeheartedly to those seeking a humane solution to plant-munching nuisance animals.
Only small negative feature is ... well, I'm well past that big 5-0 and can definitely hear the sonic output! It's right at that upper limit but it's still there. Guess I may have supersonic earsight or something, but can't guarantee that this will not be audible to some users. Since the best thing to do with this when you are working on your plot is to switch it off, in order not to drain batteries unnecessarily, this is not really a big problem - but I'm glad I sited it so its area of effect is directed away from the other plots on my site.
Still have to give it 5 stars for its sheer effectiveness. Does what it says on the box!