Now let's get something straight: Kosher slaughter is scientifically proven to be the most humane form of animal slaughter out there. This is because the knife first slices through the arteries supplying blood to the brain, and the instant loss of blood supply causes the animal to lose consciousness almost the moment it comes into contact with the knife. Now I'm sure you all know from cuts you may have experienced that the pain doesn't actually kick in for a few moments. In this case of kosher slaughter, by the time the pain begins, the animal is already unconscious and therefore doesn't feel it.
I can't speak for halal, but I do know quite a bit about kosher slaughter. In order for an animal to be kosher, the knife used must be perfectly sharp, to the point where running a fingernail up the blade will find absolutely no dents. Even the tiniest knick renders the knife unfit for use, requiring it to be sharpened, a time consuming job. The reason for this is so that the blade will slide into the neck without causing even the slightest tear, meaning it cuts straight through the arteries without obstruction, rendering the animal unconscious as explained above.
In contrast, stunning animals with electric bolts to the brain has been shown to be effective in less than 3/4 cases, meaning that the other quarter of animals die in terrible pain due to shoddy slaughtering techniques.
It's quite disingenuous of the writer of that article to attack religious slaughter without even mentioning that non-religious methods are often just as bad if not worse for the animal in terms of pain caused.