There probably some truth in ultrasonic repellents, but it probably also varies by location and species. If the device were to sweep across the effective range, it might work out pretty good, or if you had some way to change the frequency. Unlikely it would have been marketed, if it didn't work even a little. Somethings can only be cheapified so far, before becoming useless.
I built an ultrasonic cat repeller years ago (still functioning), but only works about half the time. Some cats respond to it, other ignore it, but most eventually get use to it. My Black Lab, is 100% effective, seldom even have to send him out, just his bark works. I see a cat on the security monitor, yell 'Jake, who's there', and he runs to the front door barking, cat flies.