I have both varieties. Underground wire and wireless.
I did four acres upstate on the farm. Put in by a company that installs. Absolutely calmed my nerves! They know the boundaries.
Learned them in just 24 hrs. I bush-hog paths like a race track. No way could i have fenced the property and they love to run full speed.
Connie was a deer chaser in her prime. She stops just short of the 'beeping'.
The property is remote. Just maybe a dozen cars on a summer sunday. But it just takes one yahoo speeder to kill.
I watched a neighbors dog get hit and tossed 30 feet. The driver crying. I could hear the owner calling from a 1/2 mile away an hour earlier
while i was in the garden. It was horrible.
If i had a normal fence mine would search a way to get through with a pond across the street. They used to sneak across all the time. Now they don't
even go down the drive. If i bring out the leashes they know they get to go for a swim but only with me. The first summer she got across a couple times.
So we just set it higher. (better than the hundred times she snuck off before ) We've had it for about 8 years now. She has never tested it again and
she has a high hunt drive.
I have two invisible fence units. One spare from a yard sale. I take it with me on travels. To my parents and in-laws. Where we live now has all
sorts of fence laws since we are near state parks. The approval process is insane. They like split-rail

no more than 4 ft. Chain-link needs to be
hidden from street view.
At first the neighbors were baffled that mine would run around the front yard, sun themselves, frolic and play without leaving our property.
A friend has one as well for his rescue mutts. 'Jumping' Jack was easy but their new Stella, 'all critters must die' , now has a collar the size of a car battery.
It works. Tolerance is hard to judge on some mixed breeds.
When the invisible fence guy first pulled up he said 'this will be easy'. Mine were off leash and just curious to meet him. He said the hardest are the little
nut-balls that are yanking and rolling on a leash and never have been trained are the most difficult.
Sometimes the deer chew through it. (they must feel a vibration? if they are nesting on it?) Not problem. It takes a few days before the pups figure it
out, but they still stay within the boundaries.
Only a few instances are questionable.
Severe thunderstorms. It isn't the possible power outage but something is odd with the system. But mine are
inside anyway during strong storms, as they should be, with their collars off.
I suppose this puts me in the 'swear-by-it' category. But cautious for the first few months.