I have had one of these systems for years. Put 3 different dogs through the training. Key thing, particularly with stubborn breeds is to set the collar to max stimulation level from the outset. If the system has enough sting, the dog only tests it 2 or 3 times then its done. If you use level 2, some dogs will simply tolerate it while continuing to do what they intended.
The wireless collar works differently to the buried wire. The collar received 2 radio signals, a stronger one to know that it is near a transmitter and a weaker one that is adjustable for the boundary. The system has a high/low power mode + a rotary wheel for fine tuning. When the weaker signal reaches its critical threshold, that is considered the boundary. The collar will continue the shock treatment for up to a certain time (20-30 seconds) once the animal is past the boundary. Then it will lock out until the animal comes back over the boundary. So dogs that do violate the boundary are able to return after enduring an extended zapping.
I have not yet met a dog that is willing to endure the 20 seconds more than just a couple of times. Our Minipin was extremely resistant, she would simply ignore a regular "training" collar. Once we had her sterilized she calmed down a bit...