They are effective for a number of ailments you would expect and many you wouldn't. We are at the beginning of understanding these processes better. I wouldn't think we are at a point where we can look at specific results and making general statments.
L. Reuteri 17938 + Glycerol kills C. Diff.
https://pubmed.ncbi.nlm.nih.gov/28760934/
Biogaia's Gastrus has it.
They can be very effective for C. diff infections, but beyond that it’s not as much of a wonder treatment as the initially hype suggested. There have been a lot of startups and researchers working on this space with very lackluster results (outside of C. diff, that is)