Some advantages to the use of ultrasonic pest repellents is that they do not use poisons or traps which could pose a threat to humans and pets. They are a more humane type of deterrent which also makes them an appealing choice.
Studies into how effective this type of repellent is, have shown varied results. They have proven that they have no effect on ants and spiders and have also shown little effect on cockroaches. Some kinds of pests have actually become used to the sound over time which means that they cease to become any type of a deterrent. Another problem is that the high frequency sound cannot go through furniture or walls which would render the device ineffective.
It should be noted, though, that many people have seen great results with ultrasonic pest repellents. So, if you decide to try them out, read consumer reviews and research which ones are the best to use. That way you can make an informed decision.
If you are experiencing a particularly bad pest infestation, if might be a good idea to consult a professional for advice as you may need to use a more trusted form of pest control.