In specific carb diet circles bifidus is avoided like the plague for its tendancy to overgrowth, and aggressive properties. Unfortunately I cannot site any medical testing as its knowledge that has passed to me through word of mouth, forum posts, etc etc.
However of course I have experienced it for myself. I am very sure when I took bifidus it was not a herx reaction, It lasted for the entire 4 months I was taking the offending VSL3 supplement. During that time I had joint pain, amoung many other immune related imflamatory complaints. At the time I did think it was die off, but having experienced that a few times over now I know it was far from what die off is. The biggest indication being that for me the noticeable symptoms of die off last for 3-4 days, this was in the region of 4 months.
There may be some people on the pecanbread yahoo health group who can site a more solid sourse, should it interest you.
The research that elaine (scd diet creator) had shown that l.acdicop, l.thermius, l.bulcargius (appologies for poor spelling of them!) to be the 'best' probiotic to take as the three strains are well proven, non aggressive and quite importantly work well together. I don't think elaine ever published any literiture directly on her medical findings, however she did have a masters of Science degree specialising in bio-films so I think she knew what she was on about