I would say it is slightly above average, in comparison to most store bought probios. However, PD was one of the first probios I tried 6 years ago; possibly the rest of my diet was out of whack and didn't let the probios work as effetively as they should. To be more descriptive, my stools weren't as formed as they are after using other brands (Jarrow EPS is my fav, as of now). Though I did buy them probably about three times, and I distinctly remember a slight uneasiness in my stomach immediately after swallowing--this never led to any lasting upset or problematic BMs.
I can't say I've tried the PD Ultra, or later formulations. I might give em a second chance if I find a cheap online retailer.