The Bark Training mechanisms have had mixed results from my understanding. We have a trainer for our dog and she has heard that they work, but as the dogs get used to hearing the noise, it wont matter to them anymore and they'll bark anyways.
The training method used in these barking training mechanisms are fixing a symptom (the barking). You will never get true consistent results unless you fix the cause of the barking.
If you buy one, good luck, it MIGHT work.