My experience with ThreeLac so far isn't as wonderful as the marketing materials make it sound, but I like the product so far.
My son experienced a definite die-off reaction during the first weekend that he was using it (plus Flora Balance -- Flora Balance wants other probiotics with it, and my choice was ThreeLac). He was very out of sorts, mopy, crying a bit, etc., shortly after and for a few hours after taking some for the first few days. Eventually, that wore off, and while he's continuing to take it, we've moved on to more energetic remedies to attempt to quell the yeast problems.
I think that what ThreeLac handles is overgrowth of non-fungal yeast, but I don't think ThreeLac can take out yeast in its fungal form (or maybe it just needs more time to do it...). I could be wrong here, however; this is just a hypothesis based on what I've seen so far, which is obvious die-off reaction, and some positive results, but the candida symptoms haven't completely abated -- and since we've added in other yeast remedies, we've been seeing even more results.
I think ThreeLac can be an excellent part
of a yeast handling program, but I wouldn't peg it as the ultimate solution to every yeast problem. Your mileage may vary.