Well, I myself object to the use of such devices. Please note, none of this is actually based on any real evidence, just something that is quite possible, and all common sense points that this may be true... so take this 1/2 heartedly.
Because they use ultrasound as a method of detering mosquitos, if they become in wide use in certain areas, it may also have the effect of detering other benificial animals such as bats, which use echolocation as their primary means of hunting, and the use of ultrasonic devices can blind a bat from hunting in the range at which the device operates.
If you want a good idea of what something like this can do, take a good look at the movie Daredevil, if you have seen the movie, I believe you'll remember the part where the motorcycle explodes, this effect can be similar to what happens to a bat.
Before constructing one of these, I'd look up what species of bats inhabit your area, and if their primary food is insects, such as is in the case of brown bats, in which a family (hunting group) of 10 can eat up to 1 lb. of mosquitos a night (each weighing under 1/10th of an oz that's 1600 if they ate just mosquitos) I'd suggest looking into building a bat house under your roof.
If mosquitos are that much of a problem, suggest that your neighbors do the same. And come this time next year, you won't have a mosquito problem anymore.