It takes two to tango -is it possible that the falling out was more the fault of your acquaintance than the PoI? Also, it's always possible that people can have falling outs without either party really being at fault, since certain personality types do not work well together - but the question is, was the falling out handled professionally? Did the PoI intentionally cause your acquaintance's career to be negatively affected by the falling out? Or was it a by product? If it were the former, that would be a big red flag to me, but if it were the latter then it may have been inadvertent.
Another thing to consider when you look at how easy it is to change PoIs, is how many PoIs are there at the school that you could work with? It is very helpful if it is easy to change PoIs, but you have to have someone you could change to.
Is it possible for you to visit and talk with current students in person? If not, then maybe you could talk with them via IM or on the phone, since those are less formal means of communication, they may be more willing to volunteer information. Good luck!