Another problem worth mentioning is that most probiotics do not bind super good to the intestinal wall and just get released (through the bowel) in time. One probiotic that is better than others at adhering to the intestinal walls is the one I take called HMF neuro.
I have tried about 4 different brands of probiotics and HMF neuro works the best for me. I recently tried megaflora for a month and a feel that HMF neuro is superior despite it having a lower billion count. I have tried the renew life one (50 billion) and another one not worth mentioning, and the 12.5 billion HMF neuro probiotic is more effective than the 20 billion megaflora or 50 billion renew life probiotic.
It is the only probiotic that contains HMF; human micro flora. This is harvested from other people and the body recognizes it better than other probiotics.
I would not touch threelac because it contains 3 strains and is 5 billion or less count per pill.