I had a MAJOR issue with invisible fences, including all the guilt/anxiety/fear that go along with them. I, however, moved into a neighborhood that had some pretty stringent rules about fencing. So, we decided to try the invisible fencing. We chose PETSTOP too. I liked this company because the "correction" levels could be varied; so, it's not this big 'ol whopping shock or nothing. Both Winston and Champ responded to the "correction" on the very lowest setting. Secondly, they emphasize a LOT of training and will have trainers come back multiple times if you continue to have problems (they even will pay for another company to replace the system if it doesn't work). As for the collars, I found that they were smaller and less scary looking. The one that I chose also had retractable prongs (think of the back of pen with springs), which I thought would be more comfortable.
Long story short, I made my husband try it first! He said that it definitely is a startling feeling, but not a painful one. I thought Winston, who can be the epitome of stubborn, would have a difficult time with it. However, each dog was only "corrected" twice total and it has been a WONDERFUL thing for us! Just yesterday, Winston and Champ chased a rabbit out of the yard, but stopped at the boundary!!
Just something else to consider- We are lucky to live in a nice, quiet neighborhood. There aren't too many dogs in the neighborhood and stray dogs are not the norm. So, consideration of what comes IN to your yard should also be remembered.