This product is intended to stop over-excited behavior in dogs like barking and jumping. I couldn't find any information if it could stop a dog fight. It seems to have an immediate effect, but I couldn't find any information about it being used on an attacking dog.
Please ignore my rant. The information provided by the manufacturer is zero. Null. Nothing. You even have to create an account just to able to view the Material Safety Data Sheet. There is no list of ingredients or any other technical information. They claim that it's "Clinically shown to provide quick, effective results without causing harm to pets" without even a hint of proof. This kind of marketing would be absolutely illegal in the EU and I cannot fathom how or why this is still possible in the US. end of rant
By pure chance I stumbled over this article which explains how this product was invented:
Then again, McGlone is not like most dog owners in that he is a professor at Texas Tech University who just happens to specialize in animal welfare and behavior. And, in that capacity, he just happened to have a product on hand at his house from a previous research study called Boar Mate, an odorous concoction which helps farmers with swine breeding.
So, he gave one little spritz to his dog, Toto, and immediately the dog stopped barking. Right on the spot.
McGlone said Boar Mate contains a pig pheromone [...]. In this case, the pheromone produced is androstenone, which, when secreted by male pigs, is picked up by female pigs in heat and ready to breed. It is a foul-smelling odor for humans and also affects dogs through their olfactory system.
Having shown its effectiveness in curtailing bad behavior, the product was developed and hit the stores as Stop That for both dogs and cats [...]. But, McGlone warns, it's not an end-all, beat-all to stopping dogs from barking, as the effects last just about a minute.
The "scientific research" they conducted had a sample size of 100 dogs, which is not representative at all. They have no clue why and how this pheromone affects dogs and what possible long term effects it could cause.
Furthermore, McGlone and many product reviews state that after just 1 - 2 days of "training" the dog will immediately stop the bad behavior after being shown the can. This makes me suspect (without having any means to confirm or refute) that the effect of the pheromone is extremely unpleasant for the dog, but without causing pain or any other feeling they can vocalize or express in body language. Maybe it's like a really bad dope for dogs. Who knows? The manufacturer sure doesn't...
This is the equivalent to saying "I only hit my dog with a stick for 2 days and now he stops barking and cowers whenever he sees a stick. I'll market my stick as a magical dog trainer." This product feels as bad to a dog as being hit with a stick, but since we humans see only a harmless spray can instead of a stick, we ignore the rather blatant signs of discomfort.
The only positive aspect I could see is that it's effect sets on immediately. If it could deter a dog fight (which is not proven) it would probably work quick enough to prevent further injuries.