Really disappointing product, the battery cover of the collar comes off with the slightest touch, the quality is worse than a plastic toy worth 1€ and after 2 weeks, 2 out of the 4 broke due to poor construction, there is no warranty so they are going to be thrown away.
So, prefer something more reliable

I received it yesterday and installed it today. In terms of quality, it seems very mediocre to me. The strap that holds the mechanism (Deezer) does not secure properly in the setting for the dog's neck, so when the mechanism is activated and shocks the dog, it shakes its fur and loosens the strap. The cable it includes is thicker than thread and if it is stretched even slightly during installation, it easily breaks. The installation of the cable is not easy as it needs to be placed underground 5-10cm deep, which means you have to dig. Of course, I knew this when I ordered it, but I mention it because personally, I had to dig around 400 meters around the yard to install it!

Now, as for its effectiveness, I'm still not sure because when it gets close to the cable on the external mechanism, it activates at a shorter distance than on the other side of the fence. I don't know why this happens, but I will contact the company for clarification. The truth is that it did work immediately with the dog. As soon as it starts approaching, a beeping sound warns it, and as it gets closer, the beeping becomes faster (similar to the parktronic system in a car) and in the end, it shocks the dog. However, the dog was completely confused after the first time it tried to cross the boundary and howled in pain and fear. I didn't like it at all as I felt guilty that what I was doing to it was "torture"... but on the other hand, I can't do anything else because the house I live in is in a field and doesn't have a fence, and the landlord doesn't want to spend money for this reason (or for anything else, for that matter), and I don't want to invest in such an installation that would cost me and then have to remove it when I move out in about two years. Anyway, this happened the first time and I calmed it down. We went near the cable again to see if it would react to the warning sound, and the truth is that as soon as it heard it, it didn't approach the "fence" but was anxious and kept coming close to me and didn't want to go play in the yard. At the moment I'm writing this, it is on the balcony and doesn't go anywhere else. This wasn't my intention, of course, but I will wait to see in the coming days and I will come back with a new evaluation.

And I'm back on 27/03/21 to add that the battery cover from the mechanism got lost in the field along with the battery!!!!!!!.......?????........simply tragic!!! It will continue, stay tuned.

For you again on 20/04/21, in the end, it's all going to the trash... 50€ for nothing, zero results!!!! The dog got used to it and found a way to shake its head, causing the collar's mechanism to rise to its fur, which is thicker and the prongs don't make contact with the skin, so it doesn't feel the stimulation from the electric shock. I changed the prongs with the larger ones included in the package, but the result was the same. The only thing that somewhat improves the situation is tightening the strap, but then at night, the dog can't sleep because the prongs pierce it. Moreover, even if the mechanism made contact, it didn't change anything because the dog gained momentum and jumped over the boundary-cable, ending up outside the house, risking being hit by a passing car.