Probably not what you want to hear. But since you asked:
I would never, ever, ever want one.
We live in an area where the lots are about 1.5 acres. The people on the corner have an electric fence around the whole perimeter of their lot. When we are out walking our dog, their 4 dogs will bark at us the whole time while we walk past their house, the dogs follow the perimeter of the fence. Then the owners come out and look at us...like we are the ones who are making their dogs bark.
Another set of neighbors have the fence, and every once in a while, their dog will be out unattended, and then their dog will come out to greet mine.
Another set of former neighbors had a fence, but they also had 2 really mean dogs. Yes, the fence did stop them, everytime. But when those dogs were out, I felt like we were getting charged by the dogs.
Yet another neighbor had the fence, and their dog realized that once she endured the shock, she was free to roam. So, it didn't stop her at all.
If you MUST get an electric fence...the fence is not a babysitter. Please do not leave your dog unattended. You can't control all the other things going on.
Also - the other thing I would recommend - do not have the fence go around the whole yard. Just use a part of your yard for the fence, i.e the back yard. We had neighbors who would need to drive the dogs out of the yard to go for a walk, because then they wouldn't get a shock. When the walk was over, they would drive their dog back up the driveway. (This was the owner of the 2 mean dogs...so maybe he had the setting up really high? Those dogs did stop on a dime.)
Also - don't areate the lawn, it will rip up the wire, probably in more than one place.