Before buying this, I didn't realize that some strains of bacteria used in probiotics produce histamines. When I discovered this, I looked up which ones do, and all three I discovered are used in this one. If you're sensitive to histamines or have leaky gut (which makes you sensitive to histamines), then this is not for you. According to an article on bullet proof, an overload of histamines "leads to increased inflammation and many other symptoms including: skin irritation, hives, throat tightening, increased heart rate, nasal congestion, migraines, fatigue, heartburn, reflux, and weight gain." I'm sure this can work for some people, but probably only despite the histamine-producing bacteria.
Helicobacter pylori (H. pylori) is a bacteria that causes chronic inflammation (gastritis) of the inner lining of the stomach, and also is the most common cause of ulcers worldwide. About 50% of people in the world carries or is infected with H. pylori. Common symptoms of H. pylori infection are occasional abdominal discomfort, bloating, belching or burping, and nausea and vomiting. H. pylori infection is difficult to erdicate, and treatment is with two or more antibiotics.

Notably, after someone was tagged a “persister” or “resister” clear patterns emerged on how probiotics would impact his or her indigenous microbiome and gut bacteria profile. "Although all of our probiotic-consuming volunteers showed probiotics in their stool, only some of them showed them in their gut, which is where they need to be," Eran Segal said in a statement. "If some people resist and only some people permit them, the benefits of the standard probiotics we all take can't be as universal as we once thought. These results highlight the role of the gut microbiome in driving very specific clinical differences between people." 

By eating probiotic-rich foods and maintaining good intestinal flora, a person can also help to maintain a healthy immune system. And that has real world effects: for example, in one small study of students, those who were given a fermented dairy drink (instead of milk) displayed increased production from lymphocytes -- a marker of immune response.
But what if investigators could design probiotics to treat specific individuals? Many researchers think personalized probiotics are the most promising path forward for patients with compromised gut microbiomes. Last year Jens Walter of the University of Alberta and his colleagues published a study that gives a glimpse of this potential future. The researchers decided to see what it would take to get the bacteria in a probiotic to successfully colonize the intestines of 23 volunteers. They chose a particular strain of Bifidobacterium longum that earlier studies had indicated could survive in the human intestine. In the study, the volunteers consumed either a drink containing 10 billion live B. longum bacteria or a placebo in the form of a glucose-based food additive (maltodextrin) each day for two weeks. Periodic fecal samples revealed higher than typical levels of B. longum in participants who did not consume the placebo.
While this feature contributes to the efficiency of the product, it is unclear whether this product is vegetarian like some of the other probiotics we reviewed. Therefore, if you have any dietary restrictions or needs, this may not be the best probiotic for you and may, in fact, cause additional stomach upset or irritation. It is however gluten-free.