I would suggest you try and eat better before doing this cleanse. A better diet leads to a better cleanse. Some people have reactions with psyllium which will make them bloat even more, this is per person, you may or may not. You may want to look into a parasite killer also with the probiotic. It helps clean out all those nasty guys in there. I would suggest you start a Friday since you don't know what to expect, plus drink plenty of water, absolute must. I'm not on the PB's but I'd like to try that, I'm on something similar and some days I'm running others I'm not, that is why I would suggest you try on a Friday it won't really kick til Saturday and you'll get a day jump on it.
I have yet to hear any major damage. All you are doing is dumping a lot of fiber in your system to scrub your colon walls free of all that fecal matter. When that comes out (which I've yet to see) you are on your way to feeling great!!!