I just wanted to say that in my case of dysbiotic bacteriosis which resulted from a doctor prescribing Bactrim for a Blastocystis infection, probiotics "saved the day".
It may be true that they don't establish colonies in the colon, intestinal tract and that you must keep on taking them in order to see the results but without them I would not have been able to function in my job (controlling the diarrhea) and assisting my GI tract to heal itself. They were like the army of soldiers sent in to help out that might not have stayed but were absolutely necessary. I cannot say enough about the value of probiotics. So far I have not found anything to match them in their usefulness although I may shortly be experimenting a bit with soil based organisms which also have a good reputation. I did have to experiment with dosage and sometimes needed up to 200 to 400 billion units and other times only 50 to 100 billion units a day. As I get older I will always use probiotics. To me they are as important than food.